Bugfix: getblocktemplate: Accept optional "mode" parameter not being provided

src/rpcmining.cpp

@@ -228,6 +228,10 @@ Value getblocktemplate(const Array& params, bool fHelp)
         const Value& modeval = find_value(oparam, "mode");
         if (modeval.type() == str_type)
             strMode = modeval.get_str();
+        else if (modeval.type() == null_type)
+        {
+            /* Do nothing */
+        }
         else
             throw JSONRPCError(-8, "Invalid mode");
     }