Add RequiredFieldException for better handling of missing field errors

[oatmael]

Adds an exception to allow for easier handling of missing field errors. Exposing the class & field on the exception lets users build their own error messages, which in turn allows for more human error messages to end users.

While it is currently possible to achieve this with string manipulation on the existing messages, having a distinct exception allows for much greater flexibility:

private const XERO_MISSING_FIELD_TO_HUMAN = [
  Invoice::class => [ 
   '$Contact' => 'Xero Contact',
   '$LineItems' => 'Line Items',
   ...
  ],
  ...
];

...
try {
   $this->uploadInvoice($data);
} catch (RequiredFieldException $e) {
   $human_field = self::XERO_MISSING_FIELD_TO_HUMAN[$e->getClass()][$e->getField()] ?? 'Unknown Field';
   $message = sprintf('%s is a required field, can not upload invoice.', $human_field);
   $this->setUserFlash($message);
} catch (BadRequestException $e) {
   ...
}

[calcinai]

LGTM, thanks

[oatmael]

@calcinai are there any plans to tag in the near future? I can work around this but would prefer to have canonical tags where possible

[calcinai]

Shivers sorry, will do now!