NameLUT: Raise IndexError instead of returning None (#604)

`Mapping.__get__()` should raise an `IndexError` instead of returning
`None` like `Mapping.get()` does.

Signed-off-by: Philipp Hahn <[email protected]>

Author: pmhahn

elftools/dwarf/namelut.py

@@ -112,7 +112,7 @@ def __getitem__(self, name):
         """
         if self._entries is None:
             self._entries, self._cu_headers = self._get_entries()
-        return self._entries.get(name)
+        return self._entries[name]
 
     def __iter__(self):
         """