### Question:
StringConverter implements ParameterConverter<String> { @Override public String fromString(String input) throws IllegalArgumentException { return input; } private  StringConverter(); @Override String fromString(String input); @Override Class<String> getType(); static final StringConverter INSTANCE; }### Answer:
@Test public void testFromString() throws Exception { assertThat(StringConverter.INSTANCE.fromString("hello")).isEqualTo("hello"); assertThat(StringConverter.INSTANCE.fromString("")).isEqualTo(""); assertThat(StringConverter.INSTANCE.fromString(null)).isEqualTo(null); }