This PR fixes a bug introduced in PR #2861 and reported in Issue #3108, where the unique_bodyparts and identity_scores arguments in ShelfWriter.add_prediction() were being overwritten with None due to redundant kwargs.get() calls.

These reassignments caused the method to ignore valid input arguments when passed directly. The fix removes the two lines that overwrote these parameters, restoring the correct behavior while keeping **kwargs in the signature for subclass compatibility.