fix FDG warnings

Author: vkovec

com.unity.formats.fbx/Editor/Sources/Recorders/FbxRecorder/FbxRecorder.cs

@@ -16,6 +16,11 @@ protected override void RecordFrame(RecordingSession ctx)
 
         protected override void EndRecording(RecordingSession session)
         {
+            if(session == null)
+            {
+                throw new System.ArgumentNullException("session");
+            }
+
             var settings = (FbxRecorderSettings)session.settings;
 
             foreach (var input in m_Inputs)

com.unity.formats.fbx/Editor/Sources/Recorders/FbxRecorder/FbxRecorderSettings.cs

@@ -76,6 +76,10 @@ protected override bool ValidityCheck(List<string> errors)
             if (m_AnimationInputSettings.gameObject == null)
             {
                 ok = false;
+                if(errors == null)
+                {
+                    throw new System.ArgumentNullException("errors");
+                }
                 errors.Add("No input object set");
             }