fixup

esrftaskgraph/esrftaskgraph/variable.py

@@ -326,7 +326,7 @@ class MutableVariableContainer(VariableContainer, MutableMapping):
             del self.value[name]
 
 
-class UnknownVariableError(RuntimeError):
+class MissingVariableError(RuntimeError):
     pass
 
 
@@ -361,7 +361,7 @@ class VariableContainerNamespace:
         try:
             return self._container[name]
         except (KeyError, TypeError):
-            raise UnknownVariableError(name)
+            raise MissingVariableError(name)
 
 
 class ReadOnlyVariableContainerNamespace(VariableContainerNamespace):