What needs to happen?

Currently there are a number of TODOs of the form "// TODO: Check that timestamp is valid once all runners can provide proper timestamps." in FnApiDoFnRunner. This ticket tracks fully understanding the issue and adding the suggested validation (or abandoning the TODO if it no longer makes sense or will not be done).

Issue Priority

Priority: 3 (nice-to-have improvement)

Issue Components

• Component: Python SDK
• Component: Java SDK
• Component: Go SDK
• Component: Typescript SDK
• Component: IO connector
• Component: Beam YAML
• Component: Beam examples
• Component: Beam playground
• Component: Beam katas
• Component: Website
• Component: Spark Runner
• Component: Flink Runner
• Component: Samza Runner
• Component: Twister2 Runner
• Component: Hazelcast Jet Runner
• Component: Google Cloud Dataflow Runner