getCommonRingbondNeighbour(vertex) {
    let neighbours = vertex.neighbours;

    for (var i = 0; i < neighbours.length; i++) {
      let neighbour = this.graph.vertices[neighbours[i]];

      if (ArrayHelper.containsAll(neighbour.value.rings, vertex.value.rings)) {
        return neighbour;
      }
    }

    return null;
  }
Gets the vetex sharing the edge that is the common bond of two rings.

@param {Vertex} vertex A vertex.
@returns {(Number|null)} The id of a vertex sharing the edge that is the common bond of two rings with the vertex provided or null, if none.