### Question:
DefaultExpander implements ExpressionExpander { @Override public String expand(ExpressionVariable variable, Object value) { throw new UnsupportedOperationException("expansion is not supported."); }  @Override String expand(ExpressionVariable variable, Object value);  }### Answer:
@Test void cannotBeUsed() { DefaultExpander expander = new DefaultExpander(); assertThrows(UnsupportedOperationException.class, () -> expander.expand(null, null)); }