code: private static String[] verifyImplicitOption(String[] args)
          throws ProblemException {
  
          boolean foundImplicit = false;
          for (String a : args) {
              if (a.startsWith("-implicit:")) {
                  foundImplicit = true;
                  if (!a.equals("-implicit:none")) {
                      throw new ProblemException("The only allowed setting for sjavac is -implicit:none, it is also the default.");
                  }
              }
          }
          if (foundImplicit) {
              return args;
          }
          // -implicit:none not found lets add it.
          String[] newargs = new String[args.length+1];
          System.arraycopy(args,0, newargs, 0, args.length);
          newargs[args.length] = "-implicit:none";
          return newargs;
      }
docs: Check if -implicit is supplied, if so check that it is none.
  If -implicit is not supplied, supply -implicit:none
  Only implicit:none is allowed because otherwise the multicore compilations
  and dependency tracking will be tangled up.