type fixes

react-openapi/components/FilterBar.tsx

@@ -130,6 +130,7 @@ function extractOptions(
     if (Array.isArray(df)) {
       const parts = df.map((k) => item[k]).filter((v) => v != null);
       if (parts.length > 0) return parts.join(" ");
+      return null;
     }
     const v = item[df];
     if (v != null) return String(v);