Fix $populate issue with missing responseItems for a null population context

cqf-fhir-cr/src/main/java/org/opencds/cqf/fhir/cr/plandefinition/apply/ApplyProcessor.java

@@ -127,7 +127,7 @@ protected void initApply(ApplyRequest request) {
         var version = request.resolvePathString(request.getPlanDefinition(), "version");
         if (version != null) {
             var subject = request.getSubjectId().getIdPart();
-            var formatter = new SimpleDateFormat("yyyy-MM-dd-hh.mm.ssZ");
+            var formatter = new SimpleDateFormat("yyyy-MM-dd-hh.mm.ss");
             request.getModelResolver()
                     .setValue(
                             questionnaire,

cqf-fhir-cr/src/main/java/org/opencds/cqf/fhir/cr/questionnaire/populate/ProcessItemWithContext.java

@@ -69,8 +69,13 @@ List<IBaseBackboneElement> processContextItem(PopulateRequest request, IBaseBack
                                 return null;
                             }
                         })
+                        // filtering nulls here to prevent unnecessary duplicate responseItems
                         .filter(r -> nonNull(r))
                         .collect(Collectors.toList());
+        if (populationContext.isEmpty()) {
+            // We always want to return a responseItem even if we have nothing to populate
+            populationContext.add(null);
+        }
         return populationContext.stream()
                 .map(context ->
                         processPopulationContext(request, item, contextExpression.getName(), context, profileAdapter))

cqf-fhir-cr/src/test/java/org/opencds/cqf/fhir/cr/questionnaire/populate/ProcessItemWithContextTests.java

@@ -8,13 +8,15 @@
 
 import ca.uhn.fhir.context.FhirContext;
 import ca.uhn.fhir.context.FhirVersionEnum;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import org.hl7.fhir.instance.model.api.IBase;
 import org.hl7.fhir.r4.model.Extension;
 import org.hl7.fhir.r4.model.OperationOutcome;
 import org.hl7.fhir.r4.model.Questionnaire;
 import org.hl7.fhir.r4.model.Questionnaire.QuestionnaireItemComponent;
+import org.hl7.fhir.r4.model.QuestionnaireResponse.QuestionnaireResponseItemComponent;
 import org.hl7.fhir.r4.model.StringType;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
@@ -74,4 +76,28 @@ void testMissingProfileLogsException() {
         assertTrue(operationOutcome.hasIssue());
         assertEquals(2, operationOutcome.getIssue().size());
     }
+
+    @Test
+    void testNoContextStillReturnsResponseItem() {
+        var questionnaire = new Questionnaire();
+        doReturn(FhirContext.forR4Cached()).when(repository).fhirContext();
+        var populateRequest = newPopulateRequestForVersion(FhirVersionEnum.R4, libraryEngine, questionnaire);
+        var questionnaireItem = new QuestionnaireItemComponent()
+                .setLinkId("1")
+                .setDefinition("http://hl7.org/fhir/Patient#Patient.name.given");
+        var extensions = Arrays.asList(new Extension(Constants.SDC_QUESTIONNAIRE_ITEM_POPULATION_CONTEXT));
+        questionnaireItem.setExtension(extensions);
+        var expression = new CqfExpression().setLanguage("text/cql").setExpression("%subject.name.given[0]");
+        List<IBase> expressionResults = new ArrayList<>();
+        doReturn(expression)
+                .when(expressionProcessor)
+                .getCqfExpression(populateRequest, extensions, Constants.SDC_QUESTIONNAIRE_ITEM_POPULATION_CONTEXT);
+        doReturn(expressionResults)
+                .when(expressionProcessor)
+                .getExpressionResultForItem(populateRequest, expression, "1");
+        var actual = processItemWithContext.processContextItem(populateRequest, questionnaireItem);
+        assertEquals(1, actual.size());
+        assertTrue(
+                ((QuestionnaireResponseItemComponent) actual.get(0)).getAnswer().isEmpty());
+    }
 }