I want to merge one feature branch into another, without merge commit.

Both feature branches have been branched from the same main development branch.
Let’s say I have this setup:

        |-- feature_a -- commit #1 -- commit #2
develop |
        |-- feature_b -- commit #3

And what I want to have as a result after merging is:

        |-- feature_a -- commit #1 -- commit #2 -- commit #3
develop |
        |-- feature_b -- commit #3

I tried to do the merge using following command, while feature_a is checked out:

git merge feature_b --no-commit --ff

I receive the message Automatic merge went well; stopped before committing as requested.

Unfortunately I have no explanation for this message and no idea at the moment how to resolve this “problem” in a correct way.

In my opinion the merge should have worked, escpecially regarding the fact that feature_a and feature_b were branched from the same branch and contain therefore mainly the same commit history.
Furthermore both branches face totally different sources. So the source of feature_a are fully disjunct of feature_b’s sources.

Anyone an idea?