Cherry pick shows no -m option was given error

This option specifies the parent number (starting from 1)

Up until Git 2.13 (Q2 2017), that number could be 0! (which is incorrect)

See commit b16a991 (15 Mar 2017) by Jeff King (peff).
^{(Merged by Junio C Hamano -- gitster -- in commit 9c96637, 17 Mar 2017)}

cherry-pick: detect bogus arguments to --mainline

The cherry-pick and revert commands use OPT_INTEGER() to parse --mainline. The stock parser is smart enough to reject non-numeric nonsense, but it doesn't know that parent counting starts at 1.

Worse, the value "0" is indistinguishable from the unset case, so a user who assumes the counting is 0-based will get a confusing message:

$ git cherry-pick -m 0 $merge
  error: commit ... is a merge but no -m option was given.

The correct diagnosis is that "-m 0" does not refer to the first parent ("-m 1" does).

You are trying to cherry-pick a merge. A merge is build up from at several parents. You have to supply the parent id to the merge.

You have to supply any of the followings:

-m parent-number / --mainline parent-number

Usually you cannot cherry-pick a merge because you do not know which side of the merge should be considered the mainline.

This option specifies the parent number (starting from 1) of the mainline and allows cherry-pick to replay the change relative to the specified parent.

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How to find out what are the commit parents?

Use the git show command to view the commit parents and then you can choose the parent index or the SHA-1