While trying to transition a redundant "value (not available)" option will be added to the list content of the Select List custom field

Issue Summary

If the workflow transaction screen has some mandatory (required) custom field then attempting to transition the issue in the Jira issue view without providing value for this field will end up with the redundant "value (not available)" option to be added to the list content of Select List custom field.

This is reproducible on Data Center: (yes)

Steps to Reproduce

1. Prepare your environment for replication of the issue
   • Create a Select List custom field.
   • Make it required in Field Configuration associated with your project.
   • Add a custom field to some existing screen (or create a new screen).
   • Set the screen with this custom field as a Transition View screen for some of your workflow's transitions.
   • Create a new issue (or update the existing one) and set some value for this field
2. Try to transition issues through the workflow:
   • At the screen with the required field before the transition set the value of that field to "None".
     
   • Try to move the issue to the next workflow step. The transition will be canceled and the redundant "value (not available)" option to be added to the list content of the Select List custom field.
     
   • Selecting this "value (not available)" option doesn't seem to have any negative impact. Upon transition value of a customer, the field will stay intact (i.e. on the screen above it was "First option" before the transition and will have the same value even if I select "First option (not available)").

Expected Results

No new confusing options will be added to the values of Select List custom fields.

Actual Results

A redundant "value (not available)" option is to be added to the list content of the Select List custom field in case of described scenario.

Workaround

The issue appears to be purely cosmetic and doesn't have a negative impact. According to generated HTML, the value of the redundant option is referencing the same value as it was initially set before the transition. Still, appearing of one more select option might be confusing and not expected for the end users.

<div class="field-group">
	<label for="customfield_10500">CF_SelectList(single) 
		<span class="visually-hidden">Required</span>
		<span aria-hidden="true" class="aui-icon icon-required"/></label>
	<select class="select cf-select" id="customfield_10500" name="customfield_10500">
		<option value="">None</option>
		<option value="10500">First option</option>
		<option value="10501">Second option</option>
		<option value="10502">Third option</option>
		<option selected="selected" value="10500">First option (not available)</option>
	</select>
	<div class="error">CF_SelectList(single) is required.</div>
</div>