Unable to specify tag constant

I am unable to specify a tag constant and there seems to be no way of doing it without specifying a file. I get errors such as:

 tag file 'master' does not exist

if I use the following syntax

 - put: my-docker-image
    params:
       tag: master
       build: myapi
       build_args:
            foo: bar

I need to be able to able to tag an image with a specific tag, but having to create a file for this purpose adds extra complexity to the configuration.

Is there a way to tag a put step without creating using a file? Or do I have specify this in a different location?

Start with the put-step configuration and tag behavior shown in the issue, then locate the docker-image resource's handling of tag values and its existing tests or documentation. Implement constant tags without requiring a file, and verify that the shown configuration tags the image as requested while existing tag-file behavior still works.