diff --git a/IPython/core/shellapp.py b/IPython/core/shellapp.py
index c89fa46..18b1491 100644
--- a/IPython/core/shellapp.py
+++ b/IPython/core/shellapp.py
@@ -184,15 +184,15 @@ class InteractiveShellApp(Configurable):
     module_to_run = Unicode('', config=True,
         help="Run the module as a script."
     )
-    gui = CaselessStrEnum(gui_keys, config=True,
+    gui = CaselessStrEnum(gui_keys, config=True, allow_none=True,
         help="Enable GUI event loop integration with any of {0}.".format(gui_keys)
     )
-    matplotlib = CaselessStrEnum(backend_keys,
+    matplotlib = CaselessStrEnum(backend_keys, allow_none=True,
         config=True,
         help="""Configure matplotlib for interactive use with
         the default matplotlib backend."""
     )
-    pylab = CaselessStrEnum(backend_keys,
+    pylab = CaselessStrEnum(backend_keys, allow_none=True,
         config=True,
         help="""Pre-load matplotlib and numpy for interactive use,
         selecting a particular matplotlib backend and loop integration.
diff --git a/IPython/kernel/tests/test_message_spec.py b/IPython/kernel/tests/test_message_spec.py
index 996ea7c..2ca59c7 100644
--- a/IPython/kernel/tests/test_message_spec.py
+++ b/IPython/kernel/tests/test_message_spec.py
@@ -106,7 +106,7 @@ class MimeBundle(Reference):
 
 class ExecuteReply(Reference):
     execution_count = Integer()
-    status = Enum((u'ok', u'error'))
+    status = Enum((u'ok', u'error'), allow_none=True)
     
     def check(self, d):
         Reference.check(self, d)
@@ -139,7 +139,7 @@ class ArgSpec(Reference):
 
 
 class Status(Reference):
-    execution_state = Enum((u'busy', u'idle', u'starting'))
+    execution_state = Enum((u'busy', u'idle', u'starting'), allow_none=True)
 
 
 class CompleteReply(Reference):
@@ -165,7 +165,7 @@ class KernelInfoReply(Reference):
 
 
 class IsCompleteReply(Reference):
-    status = Enum((u'complete', u'incomplete', u'invalid', u'unknown'))
+    status = Enum((u'complete', u'incomplete', u'invalid', u'unknown'), allow_none=True)
     
     def check(self, d):
         Reference.check(self, d)
@@ -187,7 +187,7 @@ Error = ExecuteReplyError
 
 
 class Stream(Reference):
-    name = Enum((u'stdout', u'stderr'))
+    name = Enum((u'stdout', u'stderr'), allow_none=True)
     text = Unicode()
 
 
diff --git a/IPython/terminal/console/interactiveshell.py b/IPython/terminal/console/interactiveshell.py
index ef97c87..a859729 100644
--- a/IPython/terminal/console/interactiveshell.py
+++ b/IPython/terminal/console/interactiveshell.py
@@ -50,7 +50,7 @@ class ZMQTerminalInteractiveShell(TerminalInteractiveShell):
     )
 
     image_handler = Enum(('PIL', 'stream', 'tempfile', 'callable'),
-                         config=True, help=
+                         config=True, allow_none=True, help=
         """
         Handler for image type output.  This is useful, for example,
         when connecting to the kernel in which pylab inline backend is