code: public static Ref createSha1Ref(String name) {
      CheckUtilities.checkStringArgument(name, "name");
  
      Ref cn = new Ref();
      cn.refType = RefType.SHA1;
      cn.name = name;
      return cn;
    }
docs: Creates a <code>Ref</code> of type <code>SHA1</code>.
  
  @param name
  The SHA1 name of this ref. The value can be a short name or the full SHA1 value. If
  the value is null, a <code>NullPointerException</code> is thrown. If the value has
  length zero, an <code>IllegalArgumentException</code> is thrown.
  @return A <code>Ref</code> instance of type <code>SHA1</code>.