code: protected String createDDMFormRuleCondition(DDMForm ddmForm) {
  		String notEmptyStatement = "not(isEmpty(getValue('%s')))";
  
  		List<DDMFormField> ddmFormFields = ddmForm.getDDMFormFields();
  
  		Stream<DDMFormField> stream = ddmFormFields.stream();
  
  		return stream.map(
  			field -> String.format(notEmptyStatement, field.getName())
  		).collect(
  			Collectors.joining(" OR ")
  		);
  	}
docs: Create a DDM form rule condition. The rule action will contain a
  'nonEmpty' statement for each field using 'OR` operator, e.g.
  <pre>
  not(isEmpty(getValue('{sizeFieldName}'))) OR
  not(isEmpty(getValue('{colorFieldName}')))
  </pre>