### Question:
StringValueFiller implements RowTransformer { @Override public Row execute(Row input) { if (input == null) { return null; } input.getColumns().forEach(e -> e.fillWithValue(this.fillValue)); return input; } StringValueFiller(String value);  StringValueFiller(); @Override Row execute(Row input);  }### Answer:
@Test public void fill() { StringValueFiller filler = new StringValueFiller(); Row input = new Row(); input.addNullColumn(0, "name"); assertTrue(input.getColumnByIndex(0).isNullValue()); Row output = filler.execute(input); assertFalse(output.getColumnByIndex(0).isNullValue()); }
@Test public void nullRow() { StringValueFiller filler = new StringValueFiller(); Row output = filler.execute(null); assertNull(output); }