[BEAM-2989] Improve coder inference for WithKeys.of(null)

• Type: Improvement
• Status: Resolved
• Priority: P3
• Resolution: Fixed
• Fix Version/s: 2.2.0
• Component/s: sdk-java-core
• Labels: Done
• Assignee: Daniel Oliveira
• Reporter: Luke Cwik
• Created: 26/Sep/17 15:41
• Updated: 06/Oct/20 21:51
• Resolved: 03/Oct/17 18:41

Description

WithKeys.<Void, String>of((Void) null)) should choose a VoidCoder as the key coder instead of erroring out.

java.lang.IllegalStateException: Unable to return a default Coder for
<transform> [PCollection]. Correct one of the following root causes:
  No Coder has been manually specified;  you may do so using .setCoder().
  Inferring a Coder from the CoderRegistry failed: Cannot provide coder for
parameterized type org.apache.beam.sdk.values.KV<K, V>: Unable to provide a
Coder for K.

WithKeysTest#testConstantKeys but using a Void key type should pass coder inference.

Issue Links

• links to: GitHub Pull Request #3922