ATLAS-2376: Fix for unitTest case in ExportServiceTest due to NPE

repository/src/main/java/org/apache/atlas/repository/impexp/ExportService.java

@@ -457,13 +457,17 @@ public class ExportService {
     }
 
     private void removeRelationshipAttributes(AtlasEntityWithExtInfo entity) {
+        if (entity.getEntity().getRelationshipAttributes() != null) {
             entity.getEntity().getRelationshipAttributes().clear();
-        if(entity.getReferredEntities() != null) {
-            for (AtlasEntity e: entity.getReferredEntities().values()) {
+        }
+        if (entity.getReferredEntities() != null) {
+            for (AtlasEntity e : entity.getReferredEntities().values()) {
+                if (e.getRelationshipAttributes() != null) {
                     e.getRelationshipAttributes().clear();
                 }
             }
         }
+    }
 
     private void addTypes(AtlasEntity entity, ExportContext context) {
         addEntityType(entity.getTypeName(), context);