### Question:
NullCheckHelper extends MatchingSectionHelper { public NullCheckHelper() { this(false); } NullCheckHelper();  NullCheckHelper(boolean testNotNull);   }### Answer:
@Test public void testNullCheckHelper() { MustacheEngine engine = MustacheEngineBuilder .newBuilder() .registerHelpers( HelpersBuilder.empty() .addIsNull() .addIsNotNull() .build()).build(); assertEquals( "NULL|NOTNULL", engine.compileMustache( "nullcheck_helper1", "{{#isNull this.getNull}}NULL{{/isNull}}|{{#isNotNull this.toString}}NOTNULL{{/isNotNull}}") .render(new Hammer())); assertEquals( "NULL", engine.compileMustache( "nullcheck_helper2", "{{#isNull this.getNull this.null}}NULL{{/isNull}}") .render(new Hammer())); assertEquals( "NULL", engine.compileMustache( "nullcheck_helper3", "{{#isNull this.getNull this.age logic=\"or\"}}NULL{{/isNull}}") .render(new Hammer())); assertEquals( "NOTNULL", engine.compileMustache( "nullcheck_helper3", "{{#isNotNull this.getNull this.age logic=\"or\"}}NOTNULL{{/isNotNull}}") .render(new Hammer())); assertEquals( "ISNULL", engine.compileMustache( "nullcheck_helper4", "{{#isNotNull this.getNull else='ISNULL'}}NOTNULL{{/isNotNull}}") .render(new Hammer())); }