When we have a handles that doesn't match any of the criteria where w…

…e can generate methods, add it as a fallback instead.

src/glue/handles.pm

@@ -16,7 +16,11 @@ class Rakudo::Guts {
             when Pair { 
                 add_handles_method_helper($metaclass, $attr_name, $expr.key, $expr.value);
             }
-            default { die sprintf("add_handles_method can't handle %s in list", $expr.WHAT); }
+            default {
+                # None of the cases we can generate methods for matched, so
+                # instead we install it as a fallback.
+                $metaclass.add_handles_fallback($metaclass, $attr_name, $expr);
+            }
         }
     }
 }