Querying for runtime process instances with list of business keys is not allowed in rest api

Querying for runtime process instances based on list of business keys is not allowed in camunda rest api POST /process-instance.

Querying by list of business keys having any difficulties? I hope querying by business keys are always faster because it has index created for this.

From the source code, it allows to query by list of process instance ids:

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But not allowing to query by list of business keys:
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I think the reason is that nobody has asked about it yet. There should not be any difficulties. You can even file a feature request and then provide a patch.