diff --git a/tensorboard/data/provider.py b/tensorboard/data/provider.py
index 024f0e7a8c..8b1d716d88 100644
--- a/tensorboard/data/provider.py
+++ b/tensorboard/data/provider.py
@@ -105,6 +105,8 @@ class DataProvider(object):
 
     Unless otherwise noted, any methods on this class may raise errors
     defined in `tensorboard.errors`, like `tensorboard.errors.NotFoundError`.
+
+    If not implemented, optional methods may return `None`.
     """
 
     def data_location(self, ctx=None, *, experiment_id):
diff --git a/tensorboard/plugins/metrics/metrics_plugin.py b/tensorboard/plugins/metrics/metrics_plugin.py
index c380e7a0de..7088eddf13 100644
--- a/tensorboard/plugins/metrics/metrics_plugin.py
+++ b/tensorboard/plugins/metrics/metrics_plugin.py
@@ -321,6 +321,11 @@ def _tags_impl(self, ctx, experiment=None):
             experiment_id=experiment,
             plugin_name=image_metadata.PLUGIN_NAME,
         )
+        # Not all data providers support tensors and/or blob sequences.
+        if histogram_mapping is None:
+            histogram_mapping = {}
+        if image_mapping is None:
+            image_mapping = {}
 
         result = {}
         result["scalars"] = _format_basic_mapping(scalar_mapping)