KeyedWorkItemCoder claims three coder arguments in getCoderArguments but only has two generic type variables

The number of coder arguments should match the number of type variables. The purpose of the method is to associate the type variables with coders.

Imported from Jira [BEAM-1008](https://issues.apache.org/jira/browse/BEAM-1008). Original Jira may contain additional context.
Reported by: kenn.

Locate KeyedWorkItemCoder and inspect getCoderArguments alongside the class's two generic type variables. Check the surrounding coder tests or test entry points, then verify that the method's returned coder count matches the type variables and that the relevant tests pass.

Written by the indexing model from the issue text.