Crash on AnimationClip::SetAdditiveReferencePose when the AnimationClip arguments for AnimationUtility.SetAdditiveReferencePose are null

How to reproduce:

1. Open the attached "IN-150969" project
2. In the menu bar, select "Bug Repro" > "AnimationUtility null clips" > "1. CrashSetAdditiveReferencePose"
3. Observe the crash

Reproducible with: 6000.0.0f1, 6000.0.82f1, 6000.3.23f1, 6000.5.10f1, 6000.6.0b10, 6000.7.0a5

Reproducible on: Ubuntu 24.04 LTS, Ubuntu 26.04 LTS (by user), Windows 10 Pro
Not reproducible on: No other environments tested

Note: Reproducible with -batchmode -nographics

First few lines of the stack trace:
#1 0x005e36b3e6ac02 in AnimationClip::SetAdditiveReferencePose(AnimationClip const*, float)
#2 0x005e36b1f989a8 in AnimationUtilityBindings::SetAdditiveReferencePose(PPtr<AnimationClip>, PPtr<AnimationClip>, float)
#3 0x005e36b2a12742 in AnimationUtility_CUSTOM_SetAdditiveReferencePose(void*, void*, float)
#4 0x000000422eab9a in (wrapper managed-to-native) UnityEditor.AnimationUtility:SetAdditiveReferencePose_Injected (intptr,intptr,single)
#5 0x000000422eaae3 in UnityEditor.AnimationUtility:SetAdditiveReferencePose (UnityEngine.AnimationClip,UnityEngine.AnimationClip,single)