Add None check to fill_template...

... as requested by @nsoranzo.

lib/galaxy/util/template.py

@@ -1,7 +1,16 @@
+"""Entry point for the usage of Cheetah templating within Galaxy."""
 from Cheetah.Template import Template
 
 
 def fill_template( template_text, context=None, **kwargs ):
+    """Fill a cheetah template out for specified context.
+
+    If template_text is None, an exception will be thrown, if context
+    is None (the default) - keyword arguments to this function will be used
+    as the context.
+    """
+    if template_text is None:
+        raise TypeError("Template text specified as None to fill_template.")
     if not context:
         context = kwargs
     return str( Template( source=template_text, searchList=[context] ) )