fix: log_classification_metrics (#1742)

Author: jaycee-li

google/cloud/aiplatform/metadata/experiment_run_resource.py

@@ -1045,6 +1045,8 @@ def log_classification_metrics(
         if (fpr or tpr or threshold) and not (fpr and tpr and threshold):
             raise ValueError("fpr, tpr, and thresholds must be set together.")
 
+        confusion_matrix = confidence_metrics = None
+
         if labels and matrix:
             if len(matrix) != len(labels):
                 raise ValueError(