Fix potential NPE when checking transform identity with null startValue

[Nepomuk5665]

Summary

This PR fixes a potential NullPointerException in AnimatableTransformParser.java when checking if transform values are identity transforms.

The Bug

The identity check methods (isAnchorPointIdentity, isPositionIdentity, isRotationIdentity, isScaleIdentity, isSkewIdentity, isSkewAngleIdentity) were accessing Keyframe.startValue without null checks, but startValue is annotated as @Nullable in Keyframe.java:

@Nullable public final T startValue;

This would cause a NullPointerException when:

1. For PointF values (anchorPoint, position): calling .equals() on null
2. For Float values (rotation, skew, skewAngle): auto-unboxing null to float
3. For ScaleXY values (scale): calling .equals() on null

Evidence That Null Values Are Expected

The existence of ensureValidRotationKeyframes() method in the same file explicitly checks for and handles null startValue:

} else if (rotation.getKeyframes().get(0).startValue == null) {
  rotation.getKeyframes().set(0, new Keyframe<>(...));
}

This demonstrates that null values can occur in practice from certain animation exports.

The Fix

Added explicit null checks before accessing startValue in all identity check methods. If startValue is null, the transform is treated as non-identity, which is the safe default behavior that preserves the transform data in the parsed result.

Testing

The fix is straightforward null-safety improvement. The behavior is:

• If startValue is null, return false (not identity) instead of crashing
• If startValue is not null, behavior is unchanged

[github-actions]

Snapshot Tests
API 23: Report Diff
API 35: Report Diff