@Override
    public Optional<FunctionDefinition> getFunctionDefinition(String name) {
        final String normalizedName = name.toUpperCase(Locale.ROOT);
        return Optional.ofNullable(normalizedFunctions.get(normalizedName));
    }
@Test
    void testGetNonExistFunction() {
        assertThat(CoreModule.INSTANCE.getFunctionDefinition("nonexist")).isEmpty();
    }