Simplify content type negotiation

aspen/http/resource.py

@@ -103,14 +103,19 @@ def use_accept_from_dispatcher(self, dispatch_accept):
 
     def negotiate_content_type(self, available, accept):
         """Given information about available and acceptable types, return a type or None.
+
+        Returns a content type if one can be negotiated.
+
+        Returns `None` if the accept header is malformed.
+
+        Raises `NegotiationFailure` if the accept header is well-formed but not
+        satisfiable given the available types.
+
         """
-        content_type = None
         try:
-            best_match = mimeparse.best_match(available, accept)
+            content_type = mimeparse.best_match(available, accept)
         except ValueError:  # unparseable Accept header
-            best_match = None
-        if best_match:
-            content_type = best_match
-        elif best_match == '':
+            content_type = None
+        if content_type == '':
             raise NegotiationFailure(accept, available)
         return content_type