@Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Argument argument1 = (Argument) o;

        if (argument != null ? !argument.equals(argument1.argument) : argument1.argument != null) return false;

        return true;
    }
@Test
  public void equalsInputNullOutputFalse() {
    // Arrange
    final Argument objectUnderTest = new Argument(null);
    final Object o = null;
    // Act
    final boolean retval = objectUnderTest.equals(o);
    // Assert result
    Assert.assertEquals(false, retval);
  }