Try It does not allow for enum query parameters without a value

When using the try it feature any enum query parameter, even if defined in YAML as required: false, will default to one of the enum values and be included in the URL constructed and used to try out an API operation. All other inputs simply contain a placeholder showing value and are excluded from the URL. There is no way to exclude the enum parameter without deleting it, whereas every other parameter can be excluded simply by not setting a value. See included screen shot.

Start with the Try It handling for enum query parameters and compare it with handling for other optional inputs. Reproduce an optional enum parameter defined with required: false, then verify that leaving it unset omits it from the constructed request URL while selected values remain usable.

Written by the indexing model from the issue text.