MINIFI-428 Create an empty FlowRegistryClient instead of a null reference.

Signed-off-by: Pierre Villard <pierre.villard.fr@gmail.com>

This closes #111.
diff --git a/minifi-nar-bundles/minifi-framework-bundle/minifi-framework/minifi-framework-core/src/main/java/org/apache/nifi/minifi/MiNiFiServer.java b/minifi-nar-bundles/minifi-framework-bundle/minifi-framework/minifi-framework-core/src/main/java/org/apache/nifi/minifi/MiNiFiServer.java
index 2bb77c7..4ef8f34 100644
--- a/minifi-nar-bundles/minifi-framework-bundle/minifi-framework/minifi-framework-core/src/main/java/org/apache/nifi/minifi/MiNiFiServer.java
+++ b/minifi-nar-bundles/minifi-framework-bundle/minifi-framework/minifi-framework-core/src/main/java/org/apache/nifi/minifi/MiNiFiServer.java
@@ -36,6 +36,7 @@
 import org.apache.nifi.minifi.status.StatusConfigReporter;
 import org.apache.nifi.minifi.status.StatusRequestException;
 import org.apache.nifi.registry.VariableRegistry;
+import org.apache.nifi.registry.flow.StandardFlowRegistryClient;
 import org.apache.nifi.reporting.BulletinRepository;
 import org.apache.nifi.services.FlowService;
 import org.apache.nifi.util.FileBasedVariableRegistry;
@@ -106,7 +107,7 @@
                     encryptor,
                     bulletinRepository,
                     variableRegistry,
-                    null
+                    new StandardFlowRegistryClient()
                     );
 
             flowService = StandardFlowService.createStandaloneInstance(