docs: protected int nextEdgeId() {
          int nextEdge = edgeCount;
          edgeCount++;
          if (edgeCount < 0)
              throw new IllegalStateException("too many edges. new edge id would be negative. " + toString());
  
          edges.ensureCapacity(((long) edgeCount + 1) * edgeEntryBytes);
          return nextEdge;
      }