diff --git a/src/main/java/org/fuin/objects4j/common/Contract.java b/src/main/java/org/fuin/objects4j/common/Contract.java
index b717c5b..3e942ad 100644
--- a/src/main/java/org/fuin/objects4j/common/Contract.java
+++ b/src/main/java/org/fuin/objects4j/common/Contract.java
@@ -23,7 +23,6 @@
 import java.util.List;
 import java.util.Set;
 
-import javax.annotation.Nullable;
 import javax.validation.ConstraintViolation;
 import javax.validation.Validation;
 import javax.validation.Validator;
diff --git a/src/main/java/org/fuin/objects4j/ui/AnnotationAnalyzer.java b/src/main/java/org/fuin/objects4j/ui/AnnotationAnalyzer.java
index 3276135..561335a 100644
--- a/src/main/java/org/fuin/objects4j/ui/AnnotationAnalyzer.java
+++ b/src/main/java/org/fuin/objects4j/ui/AnnotationAnalyzer.java
@@ -29,11 +29,11 @@
 import java.util.MissingResourceException;
 import java.util.ResourceBundle;
 
-import javax.annotation.Nullable;
 import javax.validation.constraints.NotEmpty;
 import javax.validation.constraints.NotNull;
 
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Nullable;
 
 /**
  * Wrapper for a class that has some annotations to perform some actions with.
diff --git a/src/main/java/org/fuin/objects4j/ui/ClassTextInfo.java b/src/main/java/org/fuin/objects4j/ui/ClassTextInfo.java
index 2b9cb00..411b528 100644
--- a/src/main/java/org/fuin/objects4j/ui/ClassTextInfo.java
+++ b/src/main/java/org/fuin/objects4j/ui/ClassTextInfo.java
@@ -17,10 +17,10 @@
  */
 package org.fuin.objects4j.ui;
 
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
 
 /**
  * Stores some text associated with a class.
diff --git a/src/main/java/org/fuin/objects4j/ui/FontSize.java b/src/main/java/org/fuin/objects4j/ui/FontSize.java
index 232dd15..b2e921d 100644
--- a/src/main/java/org/fuin/objects4j/ui/FontSize.java
+++ b/src/main/java/org/fuin/objects4j/ui/FontSize.java
@@ -20,10 +20,10 @@
 import java.io.Serializable;
 import java.text.DecimalFormat;
 
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
 
 /**
  * Size of a font including the unit.
diff --git a/src/main/java/org/fuin/objects4j/ui/TableColumnInfo.java b/src/main/java/org/fuin/objects4j/ui/TableColumnInfo.java
index 433ace3..870ff38 100644
--- a/src/main/java/org/fuin/objects4j/ui/TableColumnInfo.java
+++ b/src/main/java/org/fuin/objects4j/ui/TableColumnInfo.java
@@ -23,11 +23,11 @@
 import java.util.List;
 import java.util.Locale;
 
-import javax.annotation.Nullable;
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
+import org.fuin.objects4j.common.Nullable;
 
 /**
  * Table column information for a field of a class.
diff --git a/src/main/java/org/fuin/objects4j/ui/TextFieldInfo.java b/src/main/java/org/fuin/objects4j/ui/TextFieldInfo.java
index 1d0c67d..9b2b106 100644
--- a/src/main/java/org/fuin/objects4j/ui/TextFieldInfo.java
+++ b/src/main/java/org/fuin/objects4j/ui/TextFieldInfo.java
@@ -20,10 +20,10 @@
 import java.lang.reflect.Field;
 import java.util.Locale;
 
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
 
 /**
  * Information about a text field.
diff --git a/src/main/java/org/fuin/objects4j/ui/TextInfo.java b/src/main/java/org/fuin/objects4j/ui/TextInfo.java
index e6f1a2e..b125ce6 100644
--- a/src/main/java/org/fuin/objects4j/ui/TextInfo.java
+++ b/src/main/java/org/fuin/objects4j/ui/TextInfo.java
@@ -17,7 +17,7 @@
  */
 package org.fuin.objects4j.ui;
 
-import javax.annotation.concurrent.Immutable;
+import org.fuin.objects4j.common.Immutable;
 
 /**
  * Stores some text.
diff --git a/src/main/java/org/fuin/objects4j/vo/CurrencyAmount.java b/src/main/java/org/fuin/objects4j/vo/CurrencyAmount.java
index 5823d29..a4c548f 100644
--- a/src/main/java/org/fuin/objects4j/vo/CurrencyAmount.java
+++ b/src/main/java/org/fuin/objects4j/vo/CurrencyAmount.java
@@ -22,11 +22,11 @@
 import java.math.BigInteger;
 import java.util.Currency;
 
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
 import org.fuin.objects4j.ui.Label;
 import org.fuin.objects4j.ui.ShortLabel;
 
diff --git a/src/main/java/org/fuin/objects4j/vo/CurrencyAmountConverter.java b/src/main/java/org/fuin/objects4j/vo/CurrencyAmountConverter.java
index 51c7083..05b3beb 100644
--- a/src/main/java/org/fuin/objects4j/vo/CurrencyAmountConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/CurrencyAmountConverter.java
@@ -19,9 +19,10 @@
 
 import java.util.Currency;
 
-import javax.annotation.concurrent.ThreadSafe;
 import javax.persistence.AttributeConverter;
 
+import org.fuin.objects4j.common.ThreadSafe;
+
 /**
  * Converts a {@link CurrencyAmount}.
  */
diff --git a/src/main/java/org/fuin/objects4j/vo/DayOfTheWeek.java b/src/main/java/org/fuin/objects4j/vo/DayOfTheWeek.java
index 8a2633f..c47df0c 100644
--- a/src/main/java/org/fuin/objects4j/vo/DayOfTheWeek.java
+++ b/src/main/java/org/fuin/objects4j/vo/DayOfTheWeek.java
@@ -23,14 +23,14 @@
 import java.util.Collections;
 import java.util.List;
 
-import javax.annotation.Nullable;
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotEmpty;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.ConstraintViolationException;
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
+import org.fuin.objects4j.common.Nullable;
 import org.fuin.objects4j.ui.Label;
 import org.fuin.objects4j.ui.Prompt;
 import org.fuin.objects4j.ui.ShortLabel;
diff --git a/src/main/java/org/fuin/objects4j/vo/DayOfTheWeekConverter.java b/src/main/java/org/fuin/objects4j/vo/DayOfTheWeekConverter.java
index aecc879..d593f13 100644
--- a/src/main/java/org/fuin/objects4j/vo/DayOfTheWeekConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/DayOfTheWeekConverter.java
@@ -17,7 +17,7 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
+import org.fuin.objects4j.common.ThreadSafe;
 
 /**
  * Converts a {@link DayOfTheWeek} into a String and back.
diff --git a/src/main/java/org/fuin/objects4j/vo/DayOpeningHours.java b/src/main/java/org/fuin/objects4j/vo/DayOpeningHours.java
index eef45ed..efa7ced 100644
--- a/src/main/java/org/fuin/objects4j/vo/DayOpeningHours.java
+++ b/src/main/java/org/fuin/objects4j/vo/DayOpeningHours.java
@@ -21,14 +21,14 @@
 import java.util.ArrayList;
 import java.util.List;
 
-import javax.annotation.Nullable;
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotEmpty;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.ConstraintViolationException;
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
+import org.fuin.objects4j.common.Nullable;
 import org.fuin.objects4j.ui.Prompt;
 import org.fuin.objects4j.vo.HourRanges.ChangeType;
 
diff --git a/src/main/java/org/fuin/objects4j/vo/DayOpeningHoursConverter.java b/src/main/java/org/fuin/objects4j/vo/DayOpeningHoursConverter.java
index 2c554a7..3dbab63 100644
--- a/src/main/java/org/fuin/objects4j/vo/DayOpeningHoursConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/DayOpeningHoursConverter.java
@@ -17,7 +17,7 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
+import org.fuin.objects4j.common.ThreadSafe;
 
 /**
  * Converts a {@link DayOpeningHours} into a String and back.
diff --git a/src/main/java/org/fuin/objects4j/vo/EmailAddress.java b/src/main/java/org/fuin/objects4j/vo/EmailAddress.java
index e3f8901..c779abc 100644
--- a/src/main/java/org/fuin/objects4j/vo/EmailAddress.java
+++ b/src/main/java/org/fuin/objects4j/vo/EmailAddress.java
@@ -17,7 +17,6 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.Immutable;
 import javax.mail.internet.AddressException;
 import javax.mail.internet.InternetAddress;
 import javax.validation.constraints.NotNull;
@@ -25,6 +24,7 @@
 
 import org.fuin.objects4j.common.ConstraintViolationException;
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
 import org.fuin.objects4j.ui.Label;
 import org.fuin.objects4j.ui.ShortLabel;
 import org.fuin.objects4j.ui.Tooltip;
diff --git a/src/main/java/org/fuin/objects4j/vo/EmailAddressConverter.java b/src/main/java/org/fuin/objects4j/vo/EmailAddressConverter.java
index 8f123f1..d450c98 100644
--- a/src/main/java/org/fuin/objects4j/vo/EmailAddressConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/EmailAddressConverter.java
@@ -17,10 +17,11 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
 import javax.persistence.AttributeConverter;
 import javax.persistence.Converter;
 
+import org.fuin.objects4j.common.ThreadSafe;
+
 /**
  * Creates a {@link EmailAddress}.
  */
diff --git a/src/main/java/org/fuin/objects4j/vo/Hour.java b/src/main/java/org/fuin/objects4j/vo/Hour.java
index 70983c5..74d8628 100644
--- a/src/main/java/org/fuin/objects4j/vo/Hour.java
+++ b/src/main/java/org/fuin/objects4j/vo/Hour.java
@@ -19,14 +19,14 @@
 
 import java.util.regex.Pattern;
 
-import javax.annotation.Nullable;
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotEmpty;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.ConstraintViolationException;
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
+import org.fuin.objects4j.common.Nullable;
 import org.fuin.objects4j.ui.Label;
 import org.fuin.objects4j.ui.Prompt;
 import org.fuin.objects4j.ui.ShortLabel;
diff --git a/src/main/java/org/fuin/objects4j/vo/HourConverter.java b/src/main/java/org/fuin/objects4j/vo/HourConverter.java
index e94e7e0..22a5718 100644
--- a/src/main/java/org/fuin/objects4j/vo/HourConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/HourConverter.java
@@ -17,7 +17,7 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
+import org.fuin.objects4j.common.ThreadSafe;
 
 /**
  * Converts a {@link Hour} into a String and back.
diff --git a/src/main/java/org/fuin/objects4j/vo/HourRange.java b/src/main/java/org/fuin/objects4j/vo/HourRange.java
index e503682..c0e595d 100644
--- a/src/main/java/org/fuin/objects4j/vo/HourRange.java
+++ b/src/main/java/org/fuin/objects4j/vo/HourRange.java
@@ -21,14 +21,14 @@
 import java.util.BitSet;
 import java.util.List;
 
-import javax.annotation.Nullable;
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotEmpty;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.ConstraintViolationException;
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
+import org.fuin.objects4j.common.Nullable;
 import org.fuin.objects4j.ui.Label;
 import org.fuin.objects4j.ui.Prompt;
 import org.fuin.objects4j.ui.ShortLabel;
diff --git a/src/main/java/org/fuin/objects4j/vo/HourRangeConverter.java b/src/main/java/org/fuin/objects4j/vo/HourRangeConverter.java
index e080980..717904d 100644
--- a/src/main/java/org/fuin/objects4j/vo/HourRangeConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/HourRangeConverter.java
@@ -17,7 +17,7 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
+import org.fuin.objects4j.common.ThreadSafe;
 
 /**
  * Converts a {@link HourRange} into a String and back.
diff --git a/src/main/java/org/fuin/objects4j/vo/HourRanges.java b/src/main/java/org/fuin/objects4j/vo/HourRanges.java
index d4433b2..09fc0d6 100644
--- a/src/main/java/org/fuin/objects4j/vo/HourRanges.java
+++ b/src/main/java/org/fuin/objects4j/vo/HourRanges.java
@@ -24,14 +24,14 @@
 import java.util.List;
 import java.util.StringTokenizer;
 
-import javax.annotation.Nullable;
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotEmpty;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.ConstraintViolationException;
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
+import org.fuin.objects4j.common.Nullable;
 import org.fuin.objects4j.ui.Prompt;
 
 /**
diff --git a/src/main/java/org/fuin/objects4j/vo/HourRangesConverter.java b/src/main/java/org/fuin/objects4j/vo/HourRangesConverter.java
index 39fee15..c9fcc66 100644
--- a/src/main/java/org/fuin/objects4j/vo/HourRangesConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/HourRangesConverter.java
@@ -17,7 +17,7 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
+import org.fuin.objects4j.common.ThreadSafe;
 
 /**
  * Converts {@link HourRanges} into a String and back.
diff --git a/src/main/java/org/fuin/objects4j/vo/KeyValue.java b/src/main/java/org/fuin/objects4j/vo/KeyValue.java
index 0f3b30f..41f5898 100644
--- a/src/main/java/org/fuin/objects4j/vo/KeyValue.java
+++ b/src/main/java/org/fuin/objects4j/vo/KeyValue.java
@@ -21,10 +21,10 @@
 import java.util.HashMap;
 import java.util.Map;
 
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
 
 /**
  * Container for a key and a value.
diff --git a/src/main/java/org/fuin/objects4j/vo/LocaleConverter.java b/src/main/java/org/fuin/objects4j/vo/LocaleConverter.java
index 89593da..e56d71b 100644
--- a/src/main/java/org/fuin/objects4j/vo/LocaleConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/LocaleConverter.java
@@ -20,10 +20,11 @@
 import java.util.Locale;
 import java.util.StringTokenizer;
 
-import javax.annotation.concurrent.ThreadSafe;
 import javax.persistence.AttributeConverter;
 import javax.xml.bind.annotation.adapters.XmlAdapter;
 
+import org.fuin.objects4j.common.ThreadSafe;
+
 /**
  * Converts a {@link Locale} into a String and back.
  */
diff --git a/src/main/java/org/fuin/objects4j/vo/MultiDayOfTheWeek.java b/src/main/java/org/fuin/objects4j/vo/MultiDayOfTheWeek.java
index b14bedd..c565625 100644
--- a/src/main/java/org/fuin/objects4j/vo/MultiDayOfTheWeek.java
+++ b/src/main/java/org/fuin/objects4j/vo/MultiDayOfTheWeek.java
@@ -23,14 +23,14 @@
 import java.util.List;
 import java.util.StringTokenizer;
 
-import javax.annotation.Nullable;
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotEmpty;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.ConstraintViolationException;
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
+import org.fuin.objects4j.common.Nullable;
 import org.fuin.objects4j.ui.Prompt;
 
 /**
diff --git a/src/main/java/org/fuin/objects4j/vo/MultiDayOfTheWeekConverter.java b/src/main/java/org/fuin/objects4j/vo/MultiDayOfTheWeekConverter.java
index f8645d4..14645b1 100644
--- a/src/main/java/org/fuin/objects4j/vo/MultiDayOfTheWeekConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/MultiDayOfTheWeekConverter.java
@@ -17,7 +17,7 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
+import org.fuin.objects4j.common.ThreadSafe;
 
 /**
  * Converts {@link MultiDayOfTheWeek} into a String and back.
diff --git a/src/main/java/org/fuin/objects4j/vo/Password.java b/src/main/java/org/fuin/objects4j/vo/Password.java
index 48c390f..8d8d8af 100644
--- a/src/main/java/org/fuin/objects4j/vo/Password.java
+++ b/src/main/java/org/fuin/objects4j/vo/Password.java
@@ -17,11 +17,11 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
 import org.fuin.objects4j.ui.Label;
 import org.fuin.objects4j.ui.ShortLabel;
 import org.fuin.objects4j.ui.Tooltip;
diff --git a/src/main/java/org/fuin/objects4j/vo/PasswordConverter.java b/src/main/java/org/fuin/objects4j/vo/PasswordConverter.java
index adb7dbc..44a1ce5 100644
--- a/src/main/java/org/fuin/objects4j/vo/PasswordConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/PasswordConverter.java
@@ -17,10 +17,11 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
 import javax.persistence.AttributeConverter;
 import javax.persistence.Converter;
 
+import org.fuin.objects4j.common.ThreadSafe;
+
 /**
  * Creates a {@link Password}.
  */
diff --git a/src/main/java/org/fuin/objects4j/vo/PasswordSha512.java b/src/main/java/org/fuin/objects4j/vo/PasswordSha512.java
index 9115f95..7e69d52 100644
--- a/src/main/java/org/fuin/objects4j/vo/PasswordSha512.java
+++ b/src/main/java/org/fuin/objects4j/vo/PasswordSha512.java
@@ -20,12 +20,12 @@
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.ConstraintViolationException;
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
 
 /**
  * SHA-512 hashed password that is HEX encoded.
diff --git a/src/main/java/org/fuin/objects4j/vo/PasswordSha512Converter.java b/src/main/java/org/fuin/objects4j/vo/PasswordSha512Converter.java
index 4af382a..4f1c8d7 100644
--- a/src/main/java/org/fuin/objects4j/vo/PasswordSha512Converter.java
+++ b/src/main/java/org/fuin/objects4j/vo/PasswordSha512Converter.java
@@ -17,10 +17,11 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
 import javax.persistence.AttributeConverter;
 import javax.persistence.Converter;
 
+import org.fuin.objects4j.common.ThreadSafe;
+
 /**
  * Creates a {@link PasswordSha512}.
  */
diff --git a/src/main/java/org/fuin/objects4j/vo/SecurityToken.java b/src/main/java/org/fuin/objects4j/vo/SecurityToken.java
index 9084b58..6e3cddd 100644
--- a/src/main/java/org/fuin/objects4j/vo/SecurityToken.java
+++ b/src/main/java/org/fuin/objects4j/vo/SecurityToken.java
@@ -21,9 +21,10 @@
 import java.security.NoSuchAlgorithmException;
 import java.security.SecureRandom;
 
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 
+import org.fuin.objects4j.common.Immutable;
+
 /**
  * Creates a BASE64 encoded string based on a SHA1PRNG {@link SecureRandom}.
  */
diff --git a/src/main/java/org/fuin/objects4j/vo/UUIDConverter.java b/src/main/java/org/fuin/objects4j/vo/UUIDConverter.java
index ea1c7c7..c9cf29d 100644
--- a/src/main/java/org/fuin/objects4j/vo/UUIDConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/UUIDConverter.java
@@ -19,10 +19,11 @@
 
 import java.util.UUID;
 
-import javax.annotation.concurrent.ThreadSafe;
 import javax.persistence.AttributeConverter;
 import javax.xml.bind.annotation.adapters.XmlAdapter;
 
+import org.fuin.objects4j.common.ThreadSafe;
+
 /**
  * Converts a {@link UUID} into a String and back.
  */
diff --git a/src/main/java/org/fuin/objects4j/vo/UserName.java b/src/main/java/org/fuin/objects4j/vo/UserName.java
index 346e4e1..ab3eb9f 100644
--- a/src/main/java/org/fuin/objects4j/vo/UserName.java
+++ b/src/main/java/org/fuin/objects4j/vo/UserName.java
@@ -17,11 +17,11 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
 import org.fuin.objects4j.ui.Label;
 import org.fuin.objects4j.ui.ShortLabel;
 
diff --git a/src/main/java/org/fuin/objects4j/vo/UserNameConverter.java b/src/main/java/org/fuin/objects4j/vo/UserNameConverter.java
index 28a03b9..7543443 100644
--- a/src/main/java/org/fuin/objects4j/vo/UserNameConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/UserNameConverter.java
@@ -17,10 +17,11 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
 import javax.persistence.AttributeConverter;
 import javax.persistence.Converter;
 
+import org.fuin.objects4j.common.ThreadSafe;
+
 /**
  * Creates a {@link UserName}.
  */
diff --git a/src/main/java/org/fuin/objects4j/vo/ValueOfCapable.java b/src/main/java/org/fuin/objects4j/vo/ValueOfCapable.java
index 943aab9..a7dc538 100644
--- a/src/main/java/org/fuin/objects4j/vo/ValueOfCapable.java
+++ b/src/main/java/org/fuin/objects4j/vo/ValueOfCapable.java
@@ -17,7 +17,7 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.Nullable;
+import org.fuin.objects4j.common.Nullable;
 
 /**
  * Can convert a string into a type.
diff --git a/src/main/java/org/fuin/objects4j/vo/WeeklyOpeningHours.java b/src/main/java/org/fuin/objects4j/vo/WeeklyOpeningHours.java
index 44266ac..4f67638 100644
--- a/src/main/java/org/fuin/objects4j/vo/WeeklyOpeningHours.java
+++ b/src/main/java/org/fuin/objects4j/vo/WeeklyOpeningHours.java
@@ -25,14 +25,14 @@
 import java.util.Map;
 import java.util.StringTokenizer;
 
-import javax.annotation.Nullable;
-import javax.annotation.concurrent.Immutable;
 import javax.validation.constraints.NotEmpty;
 import javax.validation.constraints.NotNull;
 import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
 
 import org.fuin.objects4j.common.ConstraintViolationException;
 import org.fuin.objects4j.common.Contract;
+import org.fuin.objects4j.common.Immutable;
+import org.fuin.objects4j.common.Nullable;
 import org.fuin.objects4j.ui.Prompt;
 import org.fuin.objects4j.vo.DayOpeningHours.Change;
 
diff --git a/src/main/java/org/fuin/objects4j/vo/WeeklyOpeningHoursConverter.java b/src/main/java/org/fuin/objects4j/vo/WeeklyOpeningHoursConverter.java
index f811e5c..6cfef40 100644
--- a/src/main/java/org/fuin/objects4j/vo/WeeklyOpeningHoursConverter.java
+++ b/src/main/java/org/fuin/objects4j/vo/WeeklyOpeningHoursConverter.java
@@ -17,7 +17,7 @@
  */
 package org.fuin.objects4j.vo;
 
-import javax.annotation.concurrent.ThreadSafe;
+import org.fuin.objects4j.common.ThreadSafe;
 
 /**
  * Converts {@link WeeklyOpeningHours} into a String and back.