diff --git a/workflow/src/androidTest/java/com/google/android/fhir/workflow/FhirOperatorLibraryEvaluateTest.kt b/workflow/src/androidTest/java/com/google/android/fhir/workflow/FhirOperatorLibraryEvaluateTest.kt
index eb857c49a3..91de7a807e 100644
--- a/workflow/src/androidTest/java/com/google/android/fhir/workflow/FhirOperatorLibraryEvaluateTest.kt
+++ b/workflow/src/androidTest/java/com/google/android/fhir/workflow/FhirOperatorLibraryEvaluateTest.kt
@@ -1,5 +1,5 @@
 /*
- * Copyright 2022-2023 Google LLC
+ * Copyright 2022-2024 Google LLC
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -132,4 +132,27 @@ class FhirOperatorLibraryEvaluateTest {
 
     assertThat(results.getParameterBool("CompletedImmunization")).isTrue()
   }
+
+  @Test
+  fun evaluateImmunityCheck_shouldReturn_allEvaluatedVariables() = runBlocking {
+    val patientImmunizationHistory = load("/immunity-check/ImmunizationHistory.json") as Bundle
+    for (entry in patientImmunizationHistory.entry) {
+      fhirEngine.create(entry.resource)
+    }
+
+    // Load Library that checks if Patient has taken a vaccine
+    knowledgeManager.install(copy("/immunity-check/ImmunityCheck.json"))
+
+    // Evaluates a specific Patient
+    val results =
+      fhirOperator.evaluateLibrary(
+        libraryUrl = "http://localhost/Library/ImmunityCheck|1.0.0",
+        patientId = "d4d35004-24f8-40e4-8084-1ad75924514f",
+        expressions = null,
+      ) as Parameters
+
+    assertThat(results.hasParameter("CompletedImmunization")).isTrue()
+    assertThat(results.hasParameter("GetFinalDose")).isTrue()
+    assertThat(results.hasParameter("Patient")).isTrue()
+  }
 }
diff --git a/workflow/src/main/java/com/google/android/fhir/workflow/FhirOperator.kt b/workflow/src/main/java/com/google/android/fhir/workflow/FhirOperator.kt
index fb3e0a6c75..81ca998e40 100644
--- a/workflow/src/main/java/com/google/android/fhir/workflow/FhirOperator.kt
+++ b/workflow/src/main/java/com/google/android/fhir/workflow/FhirOperator.kt
@@ -78,11 +78,14 @@ internal constructor(
    * from a worker thread or it may throw [BlockingMainThreadException] exception.
    *
    * @param libraryUrl the url of the Library to evaluate
-   * @param expressions names of expressions in the Library to evaluate.
+   * @param expressions names of expressions in the Library to evaluate. If null the result contains
+   *   all evaluations or variables in library.
    * @return a Parameters resource that contains an evaluation result for each expression requested.
+   *   Or if expressions param is null then result contains all evaluations or variables in given
+   *   library.
    */
   @WorkerThread
-  fun evaluateLibrary(libraryUrl: String, expressions: Set<String>): IBaseParameters {
+  fun evaluateLibrary(libraryUrl: String, expressions: Set<String>?): IBaseParameters {
     return evaluateLibrary(libraryUrl, null, null, expressions)
   }
 
@@ -94,14 +97,17 @@ internal constructor(
    *
    * @param libraryUrl the url of the Library to evaluate
    * @param patientId the Id of the patient to be evaluated
-   * @param expressions names of expressions in the Library to evaluate.
-   * @return a Parameters resource that contains an evaluation result for each expression requested
+   * @param expressions names of expressions in the Library to evaluate. If null the result contains
+   *   all evaluations or variables in library.
+   * @return a Parameters resource that contains an evaluation result for each expression requested.
+   *   Or if expressions param is null then result contains all evaluations or variables in given
+   *   library.
    */
   @WorkerThread
   fun evaluateLibrary(
     libraryUrl: String,
     patientId: String,
-    expressions: Set<String>,
+    expressions: Set<String>?,
   ): IBaseParameters {
     return evaluateLibrary(libraryUrl, patientId, null, expressions)
   }
@@ -114,14 +120,17 @@ internal constructor(
    *
    * @param libraryUrl the url of the Library to evaluate
    * @param parameters list of parameters to be passed to the CQL library
-   * @param expressions names of expressions in the Library to evaluate.
-   * @return a Parameters resource that contains an evaluation result for each expression requested
+   * @param expressions names of expressions in the Library to evaluate. If null the result contains
+   *   all evaluations or variables in library.
+   * @return a Parameters resource that contains an evaluation result for each expression requested.
+   *   Or if expressions param is null then result contains all evaluations or variables in given
+   *   library.
    */
   @WorkerThread
   fun evaluateLibrary(
     libraryUrl: String,
     parameters: Parameters,
-    expressions: Set<String>,
+    expressions: Set<String>?,
   ): IBaseParameters {
     return evaluateLibrary(libraryUrl, null, parameters, expressions)
   }
@@ -135,15 +144,18 @@ internal constructor(
    * @param libraryUrl the url of the Library to evaluate
    * @param patientId the Id of the patient to be evaluated, if applicable
    * @param parameters list of parameters to be passed to the CQL library, if applicable
-   * @param expressions names of expressions in the Library to evaluate.
-   * @return a Parameters resource that contains an evaluation result for each expression requested
+   * @param expressions names of expressions in the Library to evaluate. If null the result contains
+   *   all evaluations or variables in library.
+   * @return a Parameters resource that contains an evaluation result for each expression requested.
+   *   Or if expressions param is null then result contains all evaluations or variables in given
+   *   library.
    */
   @WorkerThread
   fun evaluateLibrary(
     libraryUrl: String,
     patientId: String?,
     parameters: Parameters?,
-    expressions: Set<String>,
+    expressions: Set<String>?,
   ): IBaseParameters {
     return libraryProcessor.evaluate(
       /* url = */ libraryUrl,