Patching array join

src/array.c

@@ -1031,7 +1031,13 @@ mrb_ary_join_m(mrb_state *mrb, mrb_value ary)
 {
   mrb_value sep = mrb_nil_value();
 
-  mrb_get_args(mrb, "|S", &sep);
+  mrb_get_args(mrb, "|o", &sep);
+  if (mrb_nil_p(sep)) {
+    sep = mrb_str_to_str(mrb, sep);
+  } else if (mrb_type(sep) != MRB_TT_STRING) {
+    mrb_raise(mrb, E_TYPE_ERROR, "expected String");
+    return mrb_nil_value();
+  }
   return mrb_ary_join(mrb, ary, sep);
 }