Rollback #448

Author: Oceania2018

src/TensorFlowNET.Core/Summaries/Summary.cs

@@ -37,10 +37,13 @@ public Tensor histogram(string name, Tensor tensor, string[] collections = null,
             return val;
         }
 
-        public Tensor merge_all(string key = "summaries", string scope= null, string name= null)
+        public Tensor merge_all(string key = "summaries", string scope = null, string name = null)
         {
-            var summary_ops = ops.get_collection<ITensorOrOperation>(key, scope: scope);
-            return merge(summary_ops.Select(x => x as Tensor).ToArray(), name: name);
+            var summary_ops = ops.get_collection(key, scope: scope);
+            if (summary_ops == null)
+                return null;
+            else
+                return merge((summary_ops as List<ITensorOrOperation>).Select(x => x as Tensor).ToArray(), name: name);
         }
 
         /// <summary>