static < E > ImmutableSet < E > unsafeDelegate ( Set < E > delegate ) { switch ( delegate . size ( ) ) { case 0 : return of ( ) ; case 1 : return new SingletonImmutableSet < E > ( delegate . iterator ( ) . next ( ) ) ; default : return new RegularImmutableSet < E > ( delegate ) ; } }
the elements are known to be non - null .