LIMS-2040: Fix bug creating more than one puck

[ndg63276]

JIRA ticket: LIMS-2040

Summary:

Creating a puck, and then creating another, gives an internal server error. This was introduced by #965, as parentContainerId and parentContainerLocation are reset to empty strings between pucks, rather than nulls. The backend also doesn't sanitise the input, so the database throws an error.

Changes:

• Fix the frontend - so parentContainerId and Location are reset to nulls between pucks
• Fix the backend - coerce empty fields to nulls for those 2 fields
• Add more to the error message to help debugging in future
• NB one way to fix the error would be to define parentContainerId/Location as \d+ rather than \d*. But they need to be \d* for the case where you are deleting the parentContainer.

To test:

• Go to any proposal, any shipment (new or existing)
• Create a puck with at least one sample
• Create a second puck (without refreshing the page or clicking back or anything), check no errors occur. The payload sent should have parentContainerId as null, not "".
• Remove the frontend fix. repeat the test, check the backend fixes work :)