Fix crashes in rake tasks when a site has an empty cluster

Fixes 14659.

I reproduced the issues by following the instruction to add a new site here, and it quickly raised the crashes reported by @pijacquo during the installation of Toulouse.

added 6 commits

• 59b2efc9...d49ced42 - 4 commits from branch master
• fb52762b - Add byebug to Gemfile
• 451c2741 - Make rake tasks work for sites without cluster

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assigned to @lnussbau

added 1 commit

• d5d2dd77 - Make rake tasks work for sites without cluster

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requested review from @lnussbau

unassigned @lnussbau

nickel modulo les 2 commentaires ci-dessus

added 3 commits

• d2e6dc67 - 1 commit from branch master
• 0f39c4b0 - Add byebug to Gemfile
• 47cd4377 - Make rake tasks work for sites without cluster

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approved this merge request

ok pour moi

added 6 commits

• 47cd4377...ce120899 - 4 commits from branch master
• b8bfaa2b - Add byebug to Gemfile
• 2a5e87d2 - Make rake tasks work for sites without cluster

Compare with previous version

resolved all threads

mentioned in commit 9dfa0989

merged