#1441: Fixes for Union

Src/java/engine/src/main/java/org/opencds/cqf/cql/engine/execution/EvaluationVisitor.java

@@ -187,7 +187,7 @@ public Object visitUnion(Union elm, State state) {
                     (org.opencds.cqf.cql.engine.runtime.Interval) rightResult,
                     state);
         } else {
-            return UnionEvaluator.union(left, right, state);
+            return UnionEvaluator.union(leftResult, rightResult, state);
         }
     }
 

Src/java/engine/src/test/java/org/opencds/cqf/cql/engine/execution/TestUnion.java

@@ -2,6 +2,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.util.List;
@@ -12,10 +13,17 @@ class TestUnion extends CqlTestBase {
     @Test
     void union() {
         var results = engine.evaluate(toElmIdentifier("TestUnion"));
-        var value = results.forExpression("NullAndNull").value();
+
+        var value = results.forExpression("NullAndNullList").value();
         assertNotNull(value);
         assertTrue(((List<?>) value).isEmpty());
 
+        value = results.forExpression("NullAndNullInterval").value();
+        assertNull(value);
+
+        value = results.forExpression("NullAndNullUntyped").value();
+        assertNull(value);
+
         value = results.forExpression("NullAndEmpty").value();
         assertNotNull(value);
         assertTrue(((List<?>) value).isEmpty());

Src/java/engine/src/test/resources/org/opencds/cqf/cql/engine/execution/TestUnion.cql

@@ -1,9 +1,20 @@
 library TestUnion
 
 // expect {}
-define "NullAndNull":
+define "NullAndNullList":
     null as List<Integer> union null as List<Integer>
 
+// expect null
+define "NullAndNullInterval":
+    null as Interval<Integer> union null as Interval<Integer>
+
+// expect null
+// Based on the CQL conversion precedence rules,
+// the compiler _should have_ inferred this as Intervals
+// and not Lists.
+define "NullAndNullUntyped":
+    null union null
+
 // expect {}
 define "NullAndEmpty":
     null union {}