[tools/odmlparser] Change missing doc format Error

Author: mpsonntag

odml/tools/odmlparser.py

@@ -133,7 +133,7 @@ def from_file(self, file, doc_format=None):
 
         elif self.parser == 'RDF':
             if not doc_format:
-                raise KeyError("Format of the rdf file was not specified")
+                raise ValueError("Format of the rdf file was not specified")
 
             self.doc = RDFReader().from_file(file, doc_format)
             return self.doc