@Override
	public boolean add(Vertex v) {
		long key = v.key();
		if (!keyIndices.contains(key)) {
			if (nextIndex >= capacity) {
				grow();
			}
			keyIndices.put(key, nextIndex);
			vertices[nextIndex++] = v;
			modificationNumber++;
			return true;
		}
		return false;
	}
Adds the given vertex to the vertex set, if it does not already contain
it.

@return true if and only if the vertex was sucessfully added.
Ghidra/Framework/Generic/src/main/java/ghidra/util/graph/VertexSet.java