diff --git a/google/cloud/bigquery/v2/minimal/internal/common_v2_resources.h b/google/cloud/bigquery/v2/minimal/internal/common_v2_resources.h
index 1b4bae29d49e1..6ad69aa224bc6 100644
--- a/google/cloud/bigquery/v2/minimal/internal/common_v2_resources.h
+++ b/google/cloud/bigquery/v2/minimal/internal/common_v2_resources.h
@@ -316,6 +316,7 @@ bool operator==(Struct const& lhs, Struct const& rhs);
 
 struct ColumnData {
   std::string value;
+  // TODO(#14387): Use absl::optional instead.
   bool is_null{false};
   std::string DebugString(absl::string_view name,
                           TracingOptions const& options = {},