From 96b04c125d9547212bd07ab8db91f4a6d205f7d4 Mon Sep 17 00:00:00 2001
From: Anton Vasetenkov <antvaset@gmail.com>
Date: Tue, 23 Jul 2024 19:17:17 +1200
Subject: [PATCH] Fix list equality logic

---
 .../src/test/java/org/hl7/fhirpath/CQLOperationsR4Test.java    | 1 -
 .../resources/org/hl7/fhirpath/cql/CqlListOperatorsTest.xml    | 2 +-
 .../main/java/org/opencds/cqf/cql/engine/runtime/CqlList.java  | 3 +++
 .../opencds/cqf/cql/engine/execution/ListOperatorsTest.java    | 2 +-
 4 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/Src/java/engine-fhir/src/test/java/org/hl7/fhirpath/CQLOperationsR4Test.java b/Src/java/engine-fhir/src/test/java/org/hl7/fhirpath/CQLOperationsR4Test.java
index de0b95721..3ab7d205b 100644
--- a/Src/java/engine-fhir/src/test/java/org/hl7/fhirpath/CQLOperationsR4Test.java
+++ b/Src/java/engine-fhir/src/test/java/org/hl7/fhirpath/CQLOperationsR4Test.java
@@ -108,7 +108,6 @@ public static Object[][] dataMethod() {
             "cql/CqlListOperatorsTest/Equivalent/Equivalent123AndABC",
             "cql/CqlListOperatorsTest/Equivalent/Equivalent123AndString123",
             "cql/CqlListOperatorsTest/Equivalent/EquivalentABCAnd123",
-            "cql/CqlListOperatorsTest/Flatten/FlattenListNullAndNull",
             "cql/CqlListOperatorsTest/NotEqual/NotEqual123AndABC",
             "cql/CqlListOperatorsTest/NotEqual/NotEqual123AndString123",
             "cql/CqlListOperatorsTest/NotEqual/NotEqualABCAnd123",
diff --git a/Src/java/engine-fhir/src/test/resources/org/hl7/fhirpath/cql/CqlListOperatorsTest.xml b/Src/java/engine-fhir/src/test/resources/org/hl7/fhirpath/cql/CqlListOperatorsTest.xml
index ce3bc6364..2eef803f7 100644
--- a/Src/java/engine-fhir/src/test/resources/org/hl7/fhirpath/cql/CqlListOperatorsTest.xml
+++ b/Src/java/engine-fhir/src/test/resources/org/hl7/fhirpath/cql/CqlListOperatorsTest.xml
@@ -129,7 +129,7 @@
 	<group name="Equal">
 		<test name="EqualNullNull">
 			<expression>{null} = {null}</expression>
-			<output>null</output>
+			<output>true</output>
 		</test>
 		<test name="EqualEmptyListNull">
 			<expression>{} as List&lt;String&gt; = null</expression>
diff --git a/Src/java/engine/src/main/java/org/opencds/cqf/cql/engine/runtime/CqlList.java b/Src/java/engine/src/main/java/org/opencds/cqf/cql/engine/runtime/CqlList.java
index 63dccb26d..f4a40f4b8 100644
--- a/Src/java/engine/src/main/java/org/opencds/cqf/cql/engine/runtime/CqlList.java
+++ b/Src/java/engine/src/main/java/org/opencds/cqf/cql/engine/runtime/CqlList.java
@@ -109,6 +109,9 @@ public static Boolean equal(Iterable<?> left, Iterable<?> right, State state) {
                 if (leftObject instanceof Iterable && rightObject instanceof Iterable) {
                     return equal((Iterable<?>) leftObject, (Iterable<?>) rightObject, state);
                 }
+                if (leftObject == null && rightObject == null) {
+                    return true;
+                }
                 Boolean elementEquals = EqualEvaluator.equal(leftObject, rightObject, state);
                 if (elementEquals == null || !elementEquals) {
                     return elementEquals;
diff --git a/Src/java/engine/src/test/java/org/opencds/cqf/cql/engine/execution/ListOperatorsTest.java b/Src/java/engine/src/test/java/org/opencds/cqf/cql/engine/execution/ListOperatorsTest.java
index 7eb0045e3..18ed93304 100644
--- a/Src/java/engine/src/test/java/org/opencds/cqf/cql/engine/execution/ListOperatorsTest.java
+++ b/Src/java/engine/src/test/java/org/opencds/cqf/cql/engine/execution/ListOperatorsTest.java
@@ -164,7 +164,7 @@ void all_interval_operators() {
         assertThat(((List<?>) value).size(), is(2));
 
         value = results.forExpression("EqualNullNull").value();
-        assertThat(value, is(nullValue()));
+        assertThat(value, is(true));
 
         value = results.forExpression("EqualEmptyListNull").value();
         assertThat(value, is(nullValue()));