Regression: "required" not respected for query parameters #2403

I have this in my openapi.yaml:

parameters:
  - in: query
    name: custom_date
    required: true
    schema:
      type: string
      format: date

The auto-generated handler fails to return an error if the parameter isn't given in the request. This worked fine before, when we were using version 2.6.0, but it doesn't work on 2.7.1.

I think the bug is in runtime/bindparam.go around line 479. The code looks like this:

if !fieldsPresent {
    return nil
}

But it should look like this:

if !fieldsPresent {
    if required {
        return &RequiredParameterError{ParamName: paramName}
    } else {
        return nil
    }
}