code: public List<String> getRoleNames(final Optional<Subject> subjectOption)
      {
          final List<String> roleNames = new ArrayList<String>();
          subjectOption.ifPresent(subject -> {
              final List<? extends Role> roles = subject.getRoles();
              if (roles != null)
              {
                  for (Role role : roles)
                  {
                      if (role != null)
                      {
                          roleNames.add(role.getName());
                      }
                  }
              }
          });
  
          return roleNames;
      }
docs: Gets the role name of each role held.
  
  @param subjectOption an option for the subject
  @return a non-null list containing all role names