Index: oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/blob/MarkSweepGarbageCollector.java
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/blob/MarkSweepGarbageCollector.java	(revision 1595824)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/blob/MarkSweepGarbageCollector.java	(working copy)
@@ -38,6 +38,7 @@
 import com.google.common.base.Joiner;
 import com.google.common.base.StandardSystemProperty;
 import com.google.common.base.Stopwatch;
+import com.google.common.base.Strings;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Sets;
 import com.google.common.io.Closeables;
@@ -366,6 +367,13 @@
 
                         @Override
                         public void addReference(String blobId) {
+                            if (Strings.isNullOrEmpty(blobId)) {
+                                if (debugMode) {
+                                    LOG.trace("Ignoring blobId returned : {}", blobId);
+                                }
+                                return;
+                            }
+                            
                             if (debugMode) {
                                 LOG.trace("BlobId : {}",blobId);
                             }