code: private V get(int row, int column) {
          if (null == this.values || row >= this.values.length || null == this.values[row] || NO_VALUE == this.values[row][column]) {
              if (null != this.parentMap) {
                  return this.parentMap.get(row, column);
              }
              return null;
          }
          // something exists locally and it's not NO_VALUE, could be null
          return this.values[row][column];
      }
docs: Check the target row/column for a value. If nothing exists locally
  and a parent map exists, that will be checked.
  
  @param row
  @param column
  @return V, null if nothing exists