Origin/null display

src/main/java/io/github/linuxforhealth/core/Constants.java

@@ -26,6 +26,7 @@ public class Constants {
     public static final String HL7_BASE_PATH = "hl7/";
     public static final String FHIR_BASE_PATH = "fhir/";
     public static final String MESSAGE_BASE_PATH = "message/";
+    public static final String NULL_VAR_NAME = "NULL";
 
     private Constants() {
     }

src/main/java/io/github/linuxforhealth/hl7/data/SimpleDataTypeMapper.java

@@ -36,6 +36,7 @@ public enum SimpleDataTypeMapper {
   CODING_SYSTEM_V2_ALTERNATE(SimpleDataValueResolver.CODING_SYSTEM_V2_ALTERNATE),
   CODING_SYSTEM_V2_IDENTIFIER(SimpleDataValueResolver.CODING_SYSTEM_V2_IDENTIFIER),
   CODING_SYSTEM_V2_IS_USER_DEFINED_TABLE(SimpleDataValueResolver.CODING_SYSTEM_V2_IS_USER_DEFINED_TABLE),
+  NO_DISPLAY(SimpleDataValueResolver.NO_DISPLAY),
   SYSTEM_URL(SimpleDataValueResolver.SYSTEM_URL),
   SYSTEM_ID(SimpleDataValueResolver.SYSTEM_ID),
   PV1_DURATION_LENGTH(SimpleDataValueResolver.PV1_DURATION_LENGTH),

src/main/java/io/github/linuxforhealth/hl7/data/SimpleDataValueResolver.java

@@ -556,6 +556,10 @@ private static final SimpleCode commonCodingSystemV2 (String table, String code,
         }
     }
 
+    public static final ValueExtractor<Object, String> NO_DISPLAY = (Object value) -> {
+        if (value == "no display") { return null; };
+        return null;
+    };
     public static final ValueExtractor<Object, String> BUILD_IDENTIFIER_FROM_CWE = (Object value) -> {
         CWE newValue = ((CWE) value);
         String identifier = newValue.getCwe1_Identifier().toString();

src/main/java/io/github/linuxforhealth/hl7/util/ExpressionUtility.java

@@ -11,16 +11,15 @@
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Objects;
-
 import org.apache.commons.lang3.StringUtils;
 import org.apache.commons.lang3.tuple.ImmutablePair;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
-
 import io.github.linuxforhealth.api.EvaluationResult;
 import io.github.linuxforhealth.api.Expression;
 import io.github.linuxforhealth.api.InputDataExtractor;
 import io.github.linuxforhealth.api.ResourceValue;
+import io.github.linuxforhealth.core.Constants;
 import io.github.linuxforhealth.core.ObjectMapperUtil;
 import io.github.linuxforhealth.core.exception.DataExtractionException;
 import io.github.linuxforhealth.core.exception.RequiredConstraintFailureException;
@@ -57,6 +56,7 @@ public static ResourceEvaluationResult evaluate(InputDataExtractor dataSource,
         try {
             Map<String, Expression> expressionsToEvaluateLater = new HashMap<>();
             Map<String, EvaluationResult> localContext = new HashMap<>(context);
+            localContext.put(Constants.NULL_VAR_NAME, new EmptyEvaluationResult());
             // initialize the map and list to collect values
             List<ResourceValue> additionalResolveValues = new ArrayList<>();
             Map<String, Object> resolveValues = new HashMap<>();

src/main/resources/hl7/extension/ExtensionMeta.yml

@@ -51,8 +51,10 @@ extension_5:
          vars:
             system: SYSTEM_URL, $system_code
             code: String, MSH.9.1
+            display: $NULL
          constants:
             system_code: 'source-record-type-system'
+
 
 extension_6:
    generateList: true
@@ -67,5 +69,7 @@ extension_6:
          vars:
             system: SYSTEM_URL, $system_code
             code: String, MSH.9.2
+            display: $NULL
          constants:
-            system_code: 'source-event-trigger-system'
+            system_code: 'source-event-trigger-system'
+