Added empty matcher

hapi-fhir-server-mdm/src/main/java/ca/uhn/fhir/mdm/rules/json/MdmFieldMatchJson.java

@@ -84,6 +84,10 @@ public class MdmFieldMatchJson implements IModelJson {
 		return myMatcher;
 	}
 
+	public boolean isMatcherSupportingEmptyFields() {
+		return (getMatcher() == null) ? false : getMatcher().isMatchingEmptyFields();
+	}
+
 	public MdmFieldMatchJson setMatcher(MdmMatcherJson theMatcher) {
 		myMatcher = theMatcher;
 		return this;

hapi-fhir-server-mdm/src/main/java/ca/uhn/fhir/mdm/rules/json/MdmMatcherJson.java

@@ -66,6 +66,10 @@ public class MdmMatcherJson implements IModelJson {
 		return this;
 	}
 
+	public boolean isMatchingEmptyFields() {
+		return myAlgorithm.isMatchingEmptyFields();
+	}
+
 	public boolean match(FhirContext theFhirContext, IBase theLeftValue, IBase theRightValue) {
 		return myAlgorithm.match(theFhirContext, theLeftValue, theRightValue, myExact, myIdentifierSystem);
 	}

hapi-fhir-server-mdm/src/main/java/ca/uhn/fhir/mdm/rules/matcher/EmptyFieldMatcher.java

@@ -0,0 +1,20 @@
+package ca.uhn.fhir.mdm.rules.matcher;
+
+import ca.uhn.fhir.context.FhirContext;
+import org.hl7.fhir.instance.model.api.IBase;
+
+public class EmptyFieldMatcher implements IMdmFieldMatcher {
+
+	public EmptyFieldMatcher() {
+	}
+
+	@Override
+	public boolean matches(FhirContext theFhirContext, IBase theLeftBase, IBase theRightBase, boolean theExact, String theIdentifierSystem) {
+		for (IBase b : new IBase[] {theLeftBase, theRightBase}) {
+			if (b != null && !b.isEmpty()) {
+				return false;
+			}
+		}
+		return true;
+	}
+}

hapi-fhir-server-mdm/src/main/java/ca/uhn/fhir/mdm/rules/matcher/MdmMatcherEnum.java

@@ -48,7 +48,9 @@ public enum MdmMatcherEnum {
 	NAME_ANY_ORDER(new NameMatcher(MdmNameMatchModeEnum.ANY_ORDER)),
 	NAME_FIRST_AND_LAST(new NameMatcher(MdmNameMatchModeEnum.FIRST_AND_LAST)),
 
-	IDENTIFIER(new IdentifierMatcher());
+	IDENTIFIER(new IdentifierMatcher()),
+
+	EMPTY_FIELD(new EmptyFieldMatcher());
 
 	private final IMdmFieldMatcher myMdmFieldMatcher;
 
@@ -69,4 +71,14 @@ public enum MdmMatcherEnum {
 	public boolean match(FhirContext theFhirContext, IBase theLeftBase, IBase theRightBase, boolean theExact, String theIdentifierSystem) {
 		return myMdmFieldMatcher.matches(theFhirContext, theLeftBase, theRightBase, theExact, theIdentifierSystem);
 	}
+
+	/**
+	 * Checks if this matcher supports checks on empty fields
+	 *
+	 * @return
+	 * 		Returns true of this matcher supports empty fields and false otherwise
+	 */
+	public boolean isMatchingEmptyFields() {
+		return this == EMPTY_FIELD;
+	}
 }

hapi-fhir-server-mdm/src/main/java/ca/uhn/fhir/mdm/rules/svc/MdmResourceFieldMatcher.java

@@ -58,11 +58,11 @@ public class MdmResourceFieldMatcher {
 	/**
 	 * Compares two {@link IBaseResource}s and determines if they match, using the algorithm defined in this object's
 	 * {@link MdmFieldMatchJson}.
-	 *
+	 * <p>
 	 * In this implementation, it determines whether a given field matches between two resources. Internally this is evaluated using FhirPath. If any of the elements of theLeftResource
 	 * match any of the elements of theRightResource, will return true. Otherwise, false.
 	 *
-	 * @param theLeftResource the first {@link IBaseResource}
+	 * @param theLeftResource  the first {@link IBaseResource}
 	 * @param theRightResource the second {@link IBaseResource}
 	 * @return A boolean indicating whether they match.
 	 */
@@ -80,12 +80,19 @@ public class MdmResourceFieldMatcher {
 	@SuppressWarnings("rawtypes")
 	private MdmMatchEvaluation match(List<IBase> theLeftValues, List<IBase> theRightValues) {
 		MdmMatchEvaluation retval = new MdmMatchEvaluation(false, 0.0);
+
+		boolean isMatchingEmptyFieldValues = (theLeftValues.isEmpty() && theRightValues.isEmpty());
+		if (isMatchingEmptyFieldValues && myMdmFieldMatchJson.isMatcherSupportingEmptyFields()) {
+			return match((IBase) null, (IBase) null);
+		}
+
 		for (IBase leftValue : theLeftValues) {
 			for (IBase rightValue : theRightValues) {
 				MdmMatchEvaluation nextMatch = match(leftValue, rightValue);
 				retval = MdmMatchEvaluation.max(retval, nextMatch);
 			}
 		}
+
 		return retval;
 	}
 

hapi-fhir-server-mdm/src/test/java/ca/uhn/fhir/mdm/rules/matcher/EmptyFieldMatcherTest.java

@@ -0,0 +1,32 @@
+package ca.uhn.fhir.mdm.rules.matcher;
+
+import ca.uhn.fhir.mdm.rules.json.MdmFieldMatchJson;
+import ca.uhn.fhir.mdm.rules.json.MdmMatcherJson;
+import ca.uhn.fhir.model.primitive.StringDt;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class EmptyFieldMatcherTest extends BaseMatcherR4Test {
+
+	@Test
+	public void testEmptyFieldMatch() {
+		StringDt left = new StringDt("other value");
+		StringDt leftEmpty = new StringDt("");
+		StringDt rightEmpty = new StringDt("");
+		StringDt right = new StringDt("a value");
+		MdmMatcherJson matcher = new MdmMatcherJson().setAlgorithm(MdmMatcherEnum.EMPTY_FIELD);
+		MdmFieldMatchJson fieldMatch = new MdmFieldMatchJson().setMatcher(matcher);
+
+		assertTrue(fieldMatch.match(ourFhirContext, null, null).match);
+		assertTrue(fieldMatch.match(ourFhirContext, null, rightEmpty).match);
+		assertTrue(fieldMatch.match(ourFhirContext, leftEmpty, null).match);
+		assertTrue(fieldMatch.match(ourFhirContext, leftEmpty, rightEmpty).match);
+		assertFalse(fieldMatch.match(ourFhirContext, null, right).match);
+		assertFalse(fieldMatch.match(ourFhirContext, left, null).match);
+		assertFalse(fieldMatch.match(ourFhirContext, left, right).match);
+	}
+
+
+}

hapi-fhir-server-mdm/src/test/java/ca/uhn/fhir/mdm/rules/svc/MdmResourceFieldMatcherR4Test.java

@@ -1,7 +1,10 @@
 package ca.uhn.fhir.mdm.rules.svc;
 
 import ca.uhn.fhir.mdm.rules.json.MdmFieldMatchJson;
+import ca.uhn.fhir.mdm.rules.json.MdmMatcherJson;
+import ca.uhn.fhir.mdm.rules.json.MdmRulesJson;
 import ca.uhn.fhir.mdm.rules.json.MdmSimilarityJson;
+import ca.uhn.fhir.mdm.rules.matcher.MdmMatcherEnum;
 import ca.uhn.fhir.mdm.rules.similarity.MdmSimilarityEnum;
 import ca.uhn.fhir.parser.DataFormatException;
 import org.hl7.fhir.r4.model.Encounter;
@@ -9,6 +12,8 @@ import org.hl7.fhir.r4.model.Patient;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import java.util.Arrays;
+
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.hamcrest.core.StringStartsWith.startsWith;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -31,6 +36,34 @@ public class MdmResourceFieldMatcherR4Test extends BaseMdmRulesR4Test {
 		myJohny = buildJohny();
 	}
 
+	@Test
+	public void testEmptyPath() {
+		myMdmRulesJson = new MdmRulesJson();
+		myMdmRulesJson.setMdmTypes(Arrays.asList(new String[]{"Patient"}));
+
+		myGivenNameMatchField = new MdmFieldMatchJson()
+			.setName("empty-given")
+			.setResourceType("Patient")
+			.setResourcePath("name.given")
+			.setMatcher(new MdmMatcherJson().setAlgorithm(MdmMatcherEnum.EMPTY_FIELD));
+		myComparator = new MdmResourceFieldMatcher(ourFhirContext, myGivenNameMatchField, myMdmRulesJson);
+
+		assertFalse(myComparator.match(myJohn, myJohny).match);
+
+		myJohn.getName().clear();
+		myJohny.getName().clear();
+
+		assertTrue(myComparator.match(myJohn, myJohny).match);
+
+		myJohn = buildJohn();
+		myJohny.getName().clear();
+		assertFalse(myComparator.match(myJohn, myJohny).match);
+
+		myJohn.getName().clear();
+		myJohny = buildJohny();
+		assertFalse(myComparator.match(myJohn, myJohny).match);
+	}
+
 	@Test
 	public void testSimplePatient() {
 		Patient patient = new Patient();