The API changes made in JDK8-b89 by JDK-8011917 introduces following static method:

  Collectors.toStringJoiner(CharSequence)

while corresponding CCC request specifies following one: 

  Collectors.toStringJoiner(String)

So parameter type of toStringJoiner method has been changed to CharSequence comparing to CCC specifying String.

Although such change is quite understandable JCK Team assumes that it should be CCC approved.