Allow null pointers in ObjectMap during debugging (#1481)

Author: leekillough

src/sst/core/serialization/objectMap.h

@@ -1300,7 +1300,7 @@ class ObjectMapFundamental : public ObjectMap
     /**
        Get the value of the object as a string
      */
-    virtual std::string get() override { return SST::Core::to_string(*addr_); }
+    virtual std::string get() override { return addr_ ? SST::Core::to_string(*addr_) : "nullptr"; }
 
     /**
        Returns true as object is a fundamental