Minion will throw null point exception if protocol is null

Need fix code:
https://github.com/apache/pinot/blob/master/pinot-common/src/main/java/org/apache/pinot/common/utils/fetcher/SegmentFetcherFactory.java#L119


Start at pinot-common/src/main/java/org/apache/pinot/common/utils/fetcher/SegmentFetcherFactory.java:119 and trace how a null protocol reaches the Minion code. Reproduce the failure and inspect nearby callers or tests to establish the expected handling; done means a null protocol no longer causes a NullPointerException, with coverage for the case if applicable.

Written by the indexing model from the issue text.