A partial merge in TFileMerger creates directories that users didn't ask for

[hageboeck]

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Description

See details here:
https://root-forum.cern.ch/t/merge-only-selected-subdirectory-of-some-root-files/63867

Basically, this code should not create the directory B:

import ROOT
with ROOT.TFile("test_input.root", "recreate") as outfile:
    outfile.mkdir("A")
    outfile.mkdir("B")

file_merger = ROOT.TFileMerger(False)
file_merger.AddFile("test_input.root")
file_merger.AddObjectNames("A")
file_merger.OutputFile("test_merged.root")
merge_mode = ROOT.TFileMerger.kOnlyListed | ROOT.TFileMerger.kAll | ROOT.TFileMerger.kIncremental
file_merger.PartialMerge(merge_mode)

Reproducer

See above

ROOT version

All < 6.38

Installation method

Not relevant

Operating system

Not relevant

Additional context

No response