Re. BEAM-974 - PubSub.read/write() .withCoder requirement should raise a more informative error in Dataflow

Hello,
I'm a Google Cloud Support Specialist who recently owned a case from a platinum customer who was reporting "validation of workflow failed" internal error when attempting to use new beta SDK. Eventually, it was determined that the problem was that they weren't using .withCoder, which became required after BEAM-974[1]. They would like to request that a more informative error be thrown, as the current one is far too vague to be able to derive any useful information from. Thank you.

Regards,

Garrett Anderson
Cloud Support Specialist
Google Cloud Platform Support

[1] https://issues.apache.org/jira/browse/BEAM-974

Imported from Jira [BEAM-1662](https://issues.apache.org/jira/browse/BEAM-1662). Original Jira may contain additional context.
Reported by: gfunk.

Start by locating the PubSub.read/write() validation used by Dataflow and reproduce the workflow validation failure described in the issue. Trace the missing .withCoder case and confirm that the resulting error identifies the requirement clearly.

Written by the indexing model from the issue text.