Handle serialization of empty strings as keys

json5/lib.py

@@ -439,7 +439,7 @@ def _dump_str(obj, ensure_ascii):
 
 def _is_ident(k):
     k = str(k)
-    if not _is_id_start(k[0]) and k[0] not in (u'$', u'_'):
+    if not k or not _is_id_start(k[0]) and k[0] not in (u'$', u'_'):
         return False
     for ch in k[1:]:
         if not _is_id_continue(ch) and ch not in (u'$', u'_'):

tests/lib_test.py

@@ -422,6 +422,9 @@ def test_supplemental_unicode(self):
             # we can't test this there.
             pass
 
+    def test_empty_key(self):
+        self.assertEqual(json5.dumps({'': 'value'}), '{"": "value"}')
+
 
 if __name__ == '__main__':  # pragma: no cover
     unittest.main()