diff --git a/src/main/java/io/Mauzo/Server/Controllers/SalesCtrl.java b/src/main/java/io/Mauzo/Server/Controllers/SalesCtrl.java
index 54a1976..404b183 100644
--- a/src/main/java/io/Mauzo/Server/Controllers/SalesCtrl.java
+++ b/src/main/java/io/Mauzo/Server/Controllers/SalesCtrl.java
@@ -48,16 +48,21 @@ public Response getSalesMethod(@Context final HttpServletRequest req) {
             SalesMgt salesMgt = ServerPools.getController().acquireSales();
 
             try {
-                for (Sale sale : salesMgt.getList()) {
+                for (Sale saleAux : salesMgt.getList()) {
                     // Inicializamos los objetos a usar.
                     JsonObjectBuilder jsonObj = Json.createObjectBuilder();
     
                     // Construimos el objeto Json con los atributo de la venta.
-                    jsonObj.add("id", sale.getId());
-                    jsonObj.add("stampRef", sale.getStampRef().getTime());
-                    jsonObj.add("userId", sale.getUserId());
-                    jsonObj.add("prodId", sale.getProdId());
-                    jsonObj.add("discId", sale.getDiscId());
+                    jsonObj.add("id", saleAux.getId());
+                    jsonObj.add("stampRef", saleAux.getStampRef().getTime());
+                    jsonObj.add("userId", saleAux.getUserId());
+                    jsonObj.add("prodId", saleAux.getProdId());
+
+                    try {
+                        jsonObj.add("discId", saleAux.getDiscId());
+                    } catch (NullPointerException e) {
+                        jsonObj.addNull("discId");
+                    }
     
                     // Lo añadimos al Json Array.
                     jsonResponse.add(jsonObj);
@@ -130,12 +135,17 @@ public Response getSaleMethod(@Context final HttpServletRequest req, @PathParam(
                 jsonResponse.add("stampRef", saleAux.getStampRef().getTime());
                 jsonResponse.add("userId", saleAux.getUserId());
                 jsonResponse.add("prodId", saleAux.getProdId());
-                jsonResponse.add("discId", saleAux.getDiscId());
+                
+                try {
+                    jsonResponse.add("discId", saleAux.getDiscId());
+                } catch (NullPointerException e) {
+                    jsonResponse.addNull("discId");
+                }
 
                 response = Response.ok(jsonResponse.build().toString(), MediaType.APPLICATION_JSON);
             } catch (ManagerErrorException e) {
                 // Si no se ha encontrado, lanzamos la respuesta 404 NOT FOUND.
-                ServerApp.getLoggerSystem().info(e.toString());
+                ServerApp.getLoggerSystem().debug(e.toString());
                 response = Response.status(Status.NOT_FOUND);
             } finally {
                 // Devolvemos la conexión de ventas
@@ -177,7 +187,7 @@ public Response modifySaleMethod(@Context final HttpServletRequest req, @PathPar
                     response = Response.status(Status.OK);
                 } catch (ManagerErrorException e) {
                     // Si no se ha encontrado, lanzamos la respuesta 404 NOT FOUND.
-                    ServerApp.getLoggerSystem().info(e.toString());
+                    ServerApp.getLoggerSystem().debug(e.toString());
                     response = Response.status(Status.NOT_FOUND);
                 } finally {
                     // Devolvemos la conexión de ventas
@@ -210,7 +220,7 @@ public Response deleteSaleMethod(@Context final HttpServletRequest req, @PathPar
 
             } catch (ManagerErrorException e) {
                 // Si no se ha encontrado, lanzamos la respuesta 404 NOT FOUND.
-                ServerApp.getLoggerSystem().info(e.toString());
+                ServerApp.getLoggerSystem().debug(e.toString());
                 response = Response.status(Status.NOT_FOUND);
             } finally {
                 // Devolvemos la conexión de ventas
diff --git a/src/main/java/io/Mauzo/Server/Controllers/UsersCtrl.java b/src/main/java/io/Mauzo/Server/Controllers/UsersCtrl.java
index 40c9297..3c6a71b 100644
--- a/src/main/java/io/Mauzo/Server/Controllers/UsersCtrl.java
+++ b/src/main/java/io/Mauzo/Server/Controllers/UsersCtrl.java
@@ -71,8 +71,13 @@ public Response getLists(@Context final HttpServletRequest req) {
                     jsonObj.add("lastname", user.getLastName());
                     jsonObj.add("email", user.getEmail());
                     jsonObj.add("isAdmin", user.isAdmin());
-                    jsonObj.add("userPic", ServerUtils.byteArrayToBase64(ServerUtils.imageToByteArray(user.getUserPic(), "png")));
 
+                    try {
+                        jsonObj.add("userPic", ServerUtils.byteArrayToBase64(ServerUtils.imageToByteArray(user.getUserPic(), "png")));
+                    } catch (NullPointerException e) {
+                        jsonObj.addNull("userPic");
+                    }
+                    
                     // Lo añadimos al Json Array.
                     jsonResponse.add(jsonObj);
                 }
@@ -175,13 +180,18 @@ public Response getUser(@Context final HttpServletRequest req, @PathParam("param
                 jsonResponse.add("lastname", user.getLastName());
                 jsonResponse.add("email", user.getEmail());
                 jsonResponse.add("isAdmin", user.isAdmin());
-                jsonResponse.add("userPic", ServerUtils.byteArrayToBase64(ServerUtils.imageToByteArray(user.getUserPic(), "png")));
+               
+                try {
+                    jsonResponse.add("userPic", ServerUtils.byteArrayToBase64(ServerUtils.imageToByteArray(user.getUserPic(), "png")));
+                } catch (NullPointerException e) {
+                    jsonResponse.addNull("userPic");
+                }
 
                 // Lanzamos la respuesta 200 OK si todo ha ido bien.
                 response = Response.ok(jsonResponse.build().toString(), MediaType.APPLICATION_JSON);
             } catch (ManagerErrorException e) {
                 // Si no se ha encontrado, lanzamos la respuesta 404 NOT FOUND.
-                ServerApp.getLoggerSystem().info(e.toString());
+                ServerApp.getLoggerSystem().debug(e.toString());
                 response = Response.status(Status.NOT_FOUND);
             } finally {
                 // Devolvemos la conexión de usuarios
@@ -236,7 +246,7 @@ public Response modifyUser(@Context final HttpServletRequest req, @PathParam("pa
                     response = Response.status(Status.OK);
                 } catch (ManagerErrorException e) {
                     // Si no se ha encontrado, lanzamos la respuesta 404 NOT FOUND.
-                    ServerApp.getLoggerSystem().info(e.toString());
+                    ServerApp.getLoggerSystem().debug(e.toString());
                     response = Response.status(Status.NOT_FOUND);
                 } finally {
                    // Devolvemos la conexión de usuarios
@@ -276,7 +286,7 @@ public Response deleteUser(@Context final HttpServletRequest req, @PathParam("pa
                 response = Response.status(Status.OK);
             } catch (ManagerErrorException e) {
                 // Si no se ha encontrado, lanzamos la respuesta 404 NOT FOUND.
-                ServerApp.getLoggerSystem().info(e.toString());
+                ServerApp.getLoggerSystem().debug(e.toString());
                 response = Response.status(Status.NOT_FOUND);
             } finally {
                 // Devolvemos la conexión de usuarios
diff --git a/src/main/java/io/Mauzo/Server/ServerUtils.java b/src/main/java/io/Mauzo/Server/ServerUtils.java
index 1ff3fd6..f756906 100644
--- a/src/main/java/io/Mauzo/Server/ServerUtils.java
+++ b/src/main/java/io/Mauzo/Server/ServerUtils.java
@@ -405,7 +405,7 @@ public static byte[] byteArrayFromBase64(String base64){
      * @return Cadena de carácteres en Base64
      */
     public static String byteArrayToBase64(byte[] array){
-        return (array == null) ? "" : Base64.getEncoder().encodeToString(array);
+        return (array == null) ? null : Base64.getEncoder().encodeToString(array);
     }
 
     /**
diff --git a/src/main/java/io/Mauzo/Server/Templates/Sale.java b/src/main/java/io/Mauzo/Server/Templates/Sale.java
index 740b8dc..ebc4964 100644
--- a/src/main/java/io/Mauzo/Server/Templates/Sale.java
+++ b/src/main/java/io/Mauzo/Server/Templates/Sale.java
@@ -9,7 +9,7 @@ public class Sale {
     private Integer prodId;
     private Integer discId;
 
-    public int getId() {
+    public Integer getId() {
         return id;
     }
 
diff --git a/src/main/java/io/Mauzo/Server/Templates/User.java b/src/main/java/io/Mauzo/Server/Templates/User.java
index 6ebbcf0..4e81904 100644
--- a/src/main/java/io/Mauzo/Server/Templates/User.java
+++ b/src/main/java/io/Mauzo/Server/Templates/User.java
@@ -28,7 +28,7 @@ public void setUsername(String username) {
         this.username = username;
     }
 
-    public boolean isAdmin() {
+    public Boolean isAdmin() {
         return isAdmin;
     }