Update keras_rs/src/losses/lambda_weights.py

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: LakshmiKalaKadali

keras_rs/src/losses/lambda_weights.py

@@ -351,9 +351,10 @@ def _validate_inputs(self, labels, ranks):
     def pair_weights(self, labels, ranks):
         """
         ListMLE doesn't use pairwise weights as it's a listwise method.
-        Returns None to indicate this method is not applicable.
+        Returns a tensor of zeros to indicate no pairwise contribution.
         """
-        return None
+        shape = ops.shape(labels)
+        return ops.zeros((shape[0], shape[1], shape[1]), dtype="float32")
 
     def individual_weights(self, labels, ranks):
         """