NIFIREG-385 Returning default Revision with version 0 on RevisableEntity when revisions are disabled, so that there is always a non-null revision in case it is referenced

This closes #284.
diff --git a/nifi-registry-core/nifi-registry-docker/dockerhub/Dockerfile b/nifi-registry-core/nifi-registry-docker/dockerhub/Dockerfile
index 5fabb95..623c613 100644
--- a/nifi-registry-core/nifi-registry-docker/dockerhub/Dockerfile
+++ b/nifi-registry-core/nifi-registry-docker/dockerhub/Dockerfile
@@ -22,7 +22,7 @@
 
 ARG UID=1000
 ARG GID=1000
-ARG NIFI_REGISTRY_VERSION=1.0.0
+ARG NIFI_REGISTRY_VERSION=0.7.0
 ARG MIRROR=https://archive.apache.org/dist
 
 ENV NIFI_REGISTRY_BASE_DIR /opt/nifi-registry
diff --git a/nifi-registry-core/nifi-registry-web-api/src/main/java/org/apache/nifi/registry/web/service/StandardServiceFacade.java b/nifi-registry-core/nifi-registry-web-api/src/main/java/org/apache/nifi/registry/web/service/StandardServiceFacade.java
index f5bfb01..85be421 100644
--- a/nifi-registry-core/nifi-registry-web-api/src/main/java/org/apache/nifi/registry/web/service/StandardServiceFacade.java
+++ b/nifi-registry-core/nifi-registry-web-api/src/main/java/org/apache/nifi/registry/web/service/StandardServiceFacade.java
@@ -1191,7 +1191,11 @@
 
         // skip using the entity service if revision feature is disabled
         if (!revisionFeature.isEnabled()) {
-            return createEntity.get();
+            final T entity = createEntity.get();
+            if (entity.getRevision() == null) {
+                entity.setRevision(new RevisionInfo(null, 0L));
+            }
+            return entity;
         } else {
             try {
                 return entityService.create(requestEntity, creatorIdentity, createEntity);
@@ -1207,7 +1211,11 @@
 
         // skip using the entity service if revision feature is disabled
         if (!revisionFeature.isEnabled()) {
-            return updateEntity.get();
+            final T entity = updateEntity.get();
+            if (entity.getRevision() == null) {
+                entity.setRevision(new RevisionInfo(null, 0L));
+            }
+            return entity;
         } else {
             try {
                 return entityService.update(requestEntity, updaterIdentity, updateEntity);
@@ -1222,7 +1230,11 @@
                                                  final RevisionInfo revisionInfo, final Supplier<T> deleteEntity) {
         // skip using the entity service if revision feature is disabled
         if (!revisionFeature.isEnabled()) {
-            return deleteEntity.get();
+            final T entity = deleteEntity.get();
+            if (entity.getRevision() == null) {
+                entity.setRevision(new RevisionInfo(null, 0L));
+            }
+            return entity;
         } else {
             try {
                 return entityService.delete(entityIdentifier, revisionInfo, deleteEntity);