A possible bug about Object.setPrototypeOf().

A DESCRIPTION OF THE PROBLEM :
A DESCRIPTION OF THE PROBLEM :
#Version: jdk-13.0.1

#Testcase:
var foo = function(){
      var a = Object.setPrototypeOf("test", null);
      print(a);
};
foo();

#Command:
./nashorn/jdk-13.0.1/bin/jjs --no-syntax-extensions=true --no-deprecation-warning=true --language=es6 testcase.js

#Output:
testcase.js:2 TypeError: test is not an Object.

#Expected output:
test

#Description:
According to ES standard , when running this testcase, the output should be "test", but nashorn threw a TypeError exception：test is not an Object.
The references are as follows:
http://www.ecma-international.org/ecma-262/6.0/index.html#sec-object.setprototypeof