public T get(T o) {
		if ( o==null ) return o;
		int b = getBucket(o);
		T[] bucket = buckets[b];
		if ( bucket==null ) return null; // no bucket
		for (T e : bucket) {
			if ( e==null ) return null; // empty slot; not there
			if ( comparator.equals(e, o) ) return e;
		}
		return null;
	}
Add {@code o} to set if not there; return existing value if already
there. This method performs the same operation as {@link #add} aside from
the return value.
runtime/Java/src/org/antlr/v4/runtime/misc/Array2DHashSet.java