Add TODO on exploring `get_config` requirement for custom keras metrics.
@@ -226,6 +226,8 @@ def federated_aggregate_keras_metric(
# If type(metric) is subclass of another tf.keras.metric arguments passed
# to __init__ must include arguments expected by the superclass and
# specified in superclass get_config().
+ # TODO(b/197746608): finds a safer way of reconstructing the metric,
+ # default argument values in Metric constructors can cause problems here.
keras_metric = None
try:
# This is some trickery to reconstruct a metric object in the current
