Cannot clear update issue field post workflow function

If you have a value set (say for Resolution) setting the value back to none will not work (valuer will be ignored)

Editing:
com.atlassian.jira.plugin.workflow.UpdateIssueFieldFunctionPluginFactory:getDescriptorParams
to set the value when string is empty will fix it.

For a workaround, delete the function and add a new one with a blank value