[REF] Improve cron job handling when there is an invalid report insta…

[seamuslee001]

…nce id passed to mail_report job

Overview

This aims to better handle cron job reporting for the job.mail_report when an invalid instance id is passed

Before

When an invalid instance id e.g. 75 on the demo sites is passed to the job.mail_report you get an error like the following back

{
    "error_code": 0,
    "entity": "Job",
    "action": "mail_report",
    "is_error": 1,
    "error_message": " is not of type String"
}

which is because $optionVal is blank when passed through to getFieldValue but this is not obvious from the error message

After

You get an error message like the following

{
    "is_error": 1,
    "error_message": "Report Mail Triggered...\nDid not find a valid instance to execute"
}

ping @larssandergreen @demeritcowboy @eileenmcnaughton note it is probably easier to see what is going on if you ignore whitespace by adding ?w=1 into the PR url

[civibot]

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