config: don't crash with a config file containing only comments

mitmproxy/optmanager.py

@@ -432,6 +432,8 @@ def parse(text):
             raise exceptions.OptionsError("Could not parse options.")
     if isinstance(data, str):
         raise exceptions.OptionsError("Config error - no keys found.")
+    elif data is None:
+        return {}
     return data
 
 

test/mitmproxy/test_optmanager.py

@@ -257,6 +257,10 @@ def test_serialize():
     with pytest.raises(Exception, match="Config error"):
         optmanager.load(o2, t)
 
+    t = "# a comment"
+    optmanager.load(o2, t)
+    assert optmanager.load(o2, "foobar: '123'") == {"foobar": "123"}
+
     t = ""
     optmanager.load(o2, t)
     assert optmanager.load(o2, "foobar: '123'") == {"foobar": "123"}