guava/src/com/google/common/base/Equivalence.java
public final <S extends T> Wrapper<S> wrap(@Nullable S reference) {
    return new Wrapper<S>(this, reference);
  }
public final <S extends T> Wrapper<S> wrap(@Nullable S reference) {
    return new Wrapper<S>(this, reference);
  }
Returns a wrapper of {@code reference} that implements {@link Wrapper#equals(Object)
Object.equals()} such that {@code wrap(a).equals(wrap(b))} if and only if {@code equivalent(a,
b)}.

@since 10.0