Fix UnboundLocalError in RT-DETR loss when auxiliary_loss is False

[yashwantbezawada]

What does this PR do?

Fixes #42219

This PR fixes an UnboundLocalError that occurs in RTDetrForObjectDetectionLoss when config.auxiliary_loss is set to False.

Problem

The function RTDetrForObjectDetectionLoss in src/transformers/loss/loss_rt_detr.py always returns auxiliary_outputs at line 468, but this variable is only initialized inside the if config.auxiliary_loss: block (line 451). When auxiliary_loss=False, the variable is never initialized, causing:

UnboundLocalError: variable 'auxiliary_outputs' referenced before assignment

Solution

Initialize auxiliary_outputs = None before the conditional block (line 450) to ensure it always has a value when returned.

Changes:

• Added auxiliary_outputs = None initialization at line 450

This is a minimal, defensive fix that ensures the function works correctly regardless of the auxiliary_loss configuration.

Testing

The fix ensures that:

• When auxiliary_loss=True: auxiliary_outputs is set to the computed values (existing behavior)
• When auxiliary_loss=False: auxiliary_outputs is None (fixed behavior)

Additional context

The auxiliary_loss parameter defaults to True in RTDetrConfig, which is why this bug may not have been caught in standard testing scenarios. The bug only manifests when users explicitly set auxiliary_loss=False.

[yashwantbezawada]

Closing this PR due to branch divergence issues. The branch has accumulated 800+ changed files from main, causing unrelated test failures.

I'll create a new clean PR with only the RT-DETR fix shortly.

Issue: UnboundLocalError when auxiliary_loss=False in RT-DETR
Fix: Initialize auxiliary_outputs = None before conditional use