Clone Issue and Create Subtasks break when custom field has no context

Problem

When using the Clone Issue (or Create Subtask) Listener / Post function if there is at least one custom field that is Not configured for any context then the listener / post function will break when will try to set the default value (if there is any for that custom field)

Diagnosis

For some reason, one or more custom fields have at least ONE scheme not configured for any contexts. We should handle this case, even tho it seems to be a kind of misconfiguration, in the plugin.

Resolution

• Browse to JIRA Administration > Issues > Custom Fields.
• Look for any fields with the Available Context(s) of "Not configured for any context".
• Configure them (click on the cog icon > Configure).
• Edit the configuration.
• Select the appropriate context as per Configuring a Custom Field.
• Repeat this for all custom fields with the problem "Not configured for any context".