Stub generator doesn't escape strings with mixed single and double quotes

@interface StringAnno {
  String val()
}

@StringAnno(val = 'single quote string with "double quote string"')
class StringAnnoUser {}

import java.lang.*;
import java.io.*;
import java.net.*;
import java.util.*;
import groovy.lang.*;
import groovy.util.*;

@StringAnno(val="single quote string with "double quote string"") public class StringAnnoUser
  extends java.lang.Object  implements
    groovy.lang.GroovyObject {
public StringAnnoUser
() {}
public  groovy.lang.MetaClass getMetaClass() { return (groovy.lang.MetaClass)null;}
public  void setMetaClass(groovy.lang.MetaClass mc) { }
public  java.lang.Object invokeMethod(java.lang.String method, java.lang.Object arguments) { return null;}
public  java.lang.Object getProperty(java.lang.String property) { return null;}
public  void setProperty(java.lang.String property, java.lang.Object value) { }
}