code: @Nullable
      TObj get(int row, int column) {
          SparseArrayCompat<TObj> array = mData.get(row);
          return array == null ? null : array.get(column);
      }
docs: Get Object from matrix by row and column.
  
  @param row    item row position
  @param column item column position
  @return Object in row, column position in the matrix