code: public int getBlankCount() {
          int count = mBlankCount;
          if (count < 0) {
              mBlankCount = count = (mPropFilter.isConstant() ? 0 : 1)
                  + ((mPrev == null) ? 0 : mPrev.getBlankCount());
          }
          return count;
      }
docs: Returns the amount of non-constant list nodes up to this node.