code: @Nullable
    public InputRow transform(@Nullable final InputRow row)
    {
      if (row == null) {
        return null;
      }
  
      final InputRow transformedRow;
  
      if (transforms.isEmpty()) {
        transformedRow = row;
      } else {
        transformedRow = new TransformedInputRow(row, transforms);
      }
  
      if (valueMatcher != null) {
        rowSupplierForValueMatcher.set(transformedRow);
        if (!valueMatcher.matches()) {
          return null;
        }
      }
  
      return transformedRow;
    }
docs: Transforms an input row, or returns null if the row should be filtered out.
  
  @param row the input row