Migrating a merge based project to new tree

[Renato Botelho]

I'm working to migrate a downstream stable/12 based tree to the new git 
repository following instructions from [1].

I did a final merge from legacy repository and made sure top commits on 
both branches point to the same tree:

# git show -s --format=%T f4d0bc6aa6b9
98db7229803a5c93e3132bc661201f204487eee9
# git show -s --format=%T f262e04c92d7
98db7229803a5c93e3132bc661201f204487eee9

When I try to merge new one git refuses to merge due to unrelated 
histories.  Should I use --allow-unrelated-histories parameter?

[1] 
https://github.com/freebsd/git_conv/wiki/Migrating-merge-based-project-from-legacy-git-tree
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Renato Botelho