#2201: provide basic implementation for getComm

Author: cz4rs

src/vt/vrt/collection/balance/model/load_model.h

@@ -222,7 +222,9 @@ struct LoadModel
    *
    * \return the comm info
    */
-  virtual CommMapType getComm(PhaseOffset when) const = 0;
+  virtual CommMapType getComm([[maybe_unused]] PhaseOffset when) const {
+    return CommMapType{};
+  }
 
   /**
    * \brief Provide an estimate of the given object's load during a specified interval