fix: proof panic when proving absent path with intermediary empty tree.

[iammadab]

Encountered a panic in proof when you try to something in an non-existent subtree, when the non-existent subtree would have been in an empty tree (very very very rare case).
This pr prevents panics from happening along that path and fixes the error by returning the empty tree op

Issue being fixed or feature implemented

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Breaking Changes

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• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

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