Allow null as separator in TailOptions, per docs (#37902)
Allow null as separator in TailOptions, per docs (#37902)

To have no separator, `tail` docs specify to pass `null`, so it should be valid to pass. 

See: https://www.npmjs.com/package/tail#constructor-parameters

>separator: the line separator token (default: /[\r]{0,1}\n/ to handle linux/mac (9+)/windows). **Pass null if your file is binary there's no >line separator.**
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