Allow null copy/destroy functions

src/core/channel/channel_args.c

@@ -52,7 +52,7 @@ static grpc_arg copy_arg(const grpc_arg *src) {
       break;
     case GRPC_ARG_POINTER:
       dst.value.pointer = src->value.pointer;
-      dst.value.pointer.p = src->value.pointer.copy(src->value.pointer.p);
+      dst.value.pointer.p = src->value.pointer.copy? src->value.pointer.copy(src->value.pointer.p) : src->value.pointer.p;
       break;
   }
   return dst;
@@ -91,7 +91,9 @@ void grpc_channel_args_destroy(grpc_channel_args *a) {
       case GRPC_ARG_INTEGER:
         break;
       case GRPC_ARG_POINTER:
-        a->args[i].value.pointer.destroy(a->args[i].value.pointer.p);
+        if (a->args[i].value.pointer.destroy) {
+          a->args[i].value.pointer.destroy(a->args[i].value.pointer.p);
+        }
         break;
     }
     gpr_free(a->args[i].key);