Submitting a contribution page with 0 amount triggers PHP notices
When submitting a contribution page with 0 amount the payment processor is not set. However, the submission still tries to lookup a payment processor by ID and hits the following e-notice in CRM/Contribute/BAO/Contribution.php
:
$CRM16923AnUnreliableMethodHasBeenUserToDeterminePaymentProcessorFromContributionPage
.