} else {
        return ImmutableEnumSet.asImmutable(EnumSet.copyOf(collection));
      }
    } else {
      Iterator<E> itr = elements.iterator();
      if (itr.hasNext()) {
        EnumSet<E> enumSet = EnumSet.of(itr.next());
        Iterators.addAll(enumSet, itr);
        return ImmutableEnumSet.asImmutable(enumSet);
      } else {
        return ImmutableSet.of();
      }
    }
  }

import java.security.GeneralSecurityException;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.ArrayList;
import java.util.Collections;
import java.util.EnumSet;
import java.util.List;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;