updated docs

hapi-fhir-docs/src/main/resources/ca/uhn/hapi/fhir/docs/server_jpa_mdm/mdm_rules.md

@@ -356,6 +356,14 @@ The following algorithms are currently supported:
             </td>
             <td>If an optional "identifierSystem" is provided, then the identifiers only match when they belong to that system</td>
         </tr>     
+        <tr>
+            <td>EMPTY_FIELD</td>
+            <td>matcher</td>
+            <td>
+               Matches an empty field.
+            </td>
+            <td></td>
+        </tr>
         <tr>
             <td>JARO_WINKLER</td>
             <td>similarity</td>

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

@@ -1,5 +1,25 @@
 package ca.uhn.fhir.mdm.rules.matcher;
 
+/*-
+ * #%L
+ * HAPI FHIR - Master Data Management
+ * %%
+ * Copyright (C) 2014 - 2021 Smile CDR, Inc.
+ * %%
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * #L%
+ */
+
 import ca.uhn.fhir.context.FhirContext;
 import org.hl7.fhir.instance.model.api.IBase;