Rule builder regex options leave behind traces of options not selected

[mvdbeek]

Not a great description, but if you open the rule builder and you select add a column using regex and then you select Create column from expression replacement and enter nothing there and then you select one of the other options and look at the rule you get this JSON, which fails:

{
  "rules": [
    {
      "type": "add_column_regex",
      "target_column": 0,
      "expression": ".*",
      "replacement": "\u0000",
      "group_count": 1
    }
  ],
  "mapping": []
}

replacement: should not be in the rule