Recently, with fb42312e6c, we've added a limit to
how deeply nested data structures can be created from API requests to limit the
resulting recursion depth when processing them to prevent stack overflows.
However, this resulted in a slight inconsistency (not relevant for security)
where you may create custom variables with different nesting depth limits
depending on the exact way to create them. This change now introduces an
additional validation for custom variables consistently limiting there overall
depth. This was not done yet as part of the security fixes as this also affects
existing configuration in a way that might cause existing configuration now
fail the validation. The limit of 16 should be large enough so that should
affect none or very few users.
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