property name "_" results in empty string var name

https://github.com/swagger-api/swagger-codegen/blob/1a1016381e173f885242e35d4d449ada16433d3a/modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/PythonClientCodegen.java#L442

Consider the following snippet from FireHydrant's spec:

    "postV1PostMortemsReportsReportIdPublish": {
      "type": "object",
      "properties": {
        "_": {
          "type": "string",
          "enum": [
            "true"
          ]
        },

This results in the generated variable name being empty; e.g.,

def __init__(self, =None, user_ids=None, team_ids=None, _configuration=None): # noqa: E501

(Note the empty variable name for the first parameter after self.)

I think the line above is what causes this/where it needs to be protected against, but I'm not positive. (There also may be some more appropriate place to protect against this - I haven't looked up all the places where it is called.)

Start in modules/swagger-codegen/src/main/java/io/swagger/codegen/languages/PythonClientCodegen.java at line 442, then inspect the places that call the relevant name-generation logic. Reproduce the FireHydrant-style property named "_" and verify that generated Python constructor parameters always have nonempty names, without breaking the other parameters.