modified Environment to send a specific error when no external brains are in the environment

python/unityagents/environment.py

         value = {} if value is None else value
         if self._loaded and not self._global_done and self._global_done is not None:
             if isinstance(action, (int, np.int_, float, np.float_, list, np.ndarray)):
-                if self._num_external_brains > 1:
+                if self._num_external_brains == 1:
+                    action = {self._external_brain_names[0]: action}
+                elif self._num_external_brains > 1:
-                    action = {self._external_brain_names[0]: action}
+                    raise UnityActionException(
+                        "There are no external brains in the environment, " 
+                        "step cannot take an action input")
+                    
-                if self._num_external_brains > 1:
+                if self._num_external_brains == 1:
+                    memory = {self._external_brain_names[0]: memory}
+                elif self._num_external_brains > 1:
-                    memory = {self._external_brain_names[0]: memory}
+                    raise UnityActionException(
+                        "There are no external brains in the environment, " 
+                        "step cannot take a memory input")
-                if self._num_external_brains > 1:
+                if self._num_external_brains == 1:
+                    value = {self._external_brain_names[0]: value}
+                elif self._num_external_brains > 1:  
-                    value = {self._external_brain_names[0]: value}
+                    raise UnityActionException(
+                        "There are no external brains in the environment, " 
+                        "step cannot take a value input")
+
+            for brain_name in action.keys() + memory.keys() + value.keys():
+                if brain_name not in self._external_brain_names:
+                    raise UnityActionException(
+                        "The name {0} does not correspond to an external brain "
+                        "in the environment". format(brain_name))
 
             for b in self._external_brain_names:
                 n_agent = len(self._data[b].agents)

unity-environment/Assets/ML-Agents/Scripts/Monitor.cs

                     }
                     if (valsSum == 0)
                     {
-                        Debug.LogError(string.Format("The value for key {0} must be "
+                        Debug.LogError(string.Format("The Monitor value for key {0} must be "
                                 + "a list or array of positive values and cannot be empty.", key));
                     }
                     else