stream: make null an invalid chunk to write in object mode
Checklist
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tests and code linting passes -
a test and/or benchmark is included -
documentation is changed or added (current documentation implies this behavior) -
the commit message follows commit guidelines
Affected core subsystem(s)
Description of change
as discussed by @nodejs/streams
this harmonizes behavior between readable, writable, and transform streams so that they all handle nulls in object mode the same way by considering them invalid chunks.