mrb_check_convert_type should always return nil on error

src/object.c

@@ -327,8 +327,7 @@ mrb_check_to_integer(mrb_state *mrb, mrb_value val, const char *method)
 
     if (mrb_type(val) == MRB_TT_FIXNUM) return val;
     v = convert_type(mrb, val, "Integer", method, FALSE);
-    if (mrb_nil_p(v)) return (v);
-    if (!mrb_obj_is_kind_of(mrb, v, mrb_obj_class(mrb, v))) {
+    if (mrb_nil_p(v) || mrb_type(v) != MRB_TT_FIXNUM) {
       return mrb_nil_value();
     }
     return v;
@@ -343,7 +342,7 @@ mrb_convert_type(mrb_state *mrb, mrb_value val, mrb_int type, const char *tname,
   v = convert_type(mrb, val, tname, method, 1/*Qtrue*/);
   if (mrb_type(v) != type) {
     mrb_raise(mrb, E_TYPE_ERROR, "%s cannot be converted to %s by #%s",
-     mrb_obj_classname(mrb, val), tname, method);
+	      mrb_obj_classname(mrb, val), tname, method);
   }
   return v;
 }
@@ -353,14 +352,9 @@ mrb_check_convert_type(mrb_state *mrb, mrb_value val, mrb_int type, const char *
 {
   mrb_value v;
 
-  /* always convert T_DATA */
   if (mrb_type(val) == type && type != MRB_TT_DATA) return val;
   v = convert_type(mrb, val, tname, method, 0/*Qfalse*/);
-  if (mrb_nil_p(v)) return mrb_nil_value();
-  if (mrb_type(v) != type) {
-    mrb_raise(mrb, E_TYPE_ERROR, "%s#%s should return %s",
-     mrb_obj_classname(mrb, val), method, tname);
-  }
+  if (mrb_nil_p(v) || mrb_type(v) != type) return mrb_nil_value();
   return v;
 }