code: function createChecks(fieldDefinition, fieldName) {
  	const severity = propertyHelper.getSeverity(fieldDefinition);
  
  	let defaultValue;
  	if (fieldDefinition.defaultValue !== undefined) {
  		defaultValue = stringToBoolean(fieldDefinition.defaultValue);
  		if (defaultValue === undefined) {
  			throw {
  				errorCode: 'NOT_BOOLEAN',
  				severity: severity,
  				value: fieldDefinition.defaultValue,
  				message: 'The defaultValue in the fieldDefinition is not a valid boolean value.'
  			};
  		}
  	}
  
  	let errorInfo = {
  		severity: severity,
  		errorCode: 'NOT_BOOLEAN'
  	};
  
  	return functionHelper.getParserCheck(errorInfo, stringToBoolean, fieldName, defaultValue);
  }
docs: Create a function which
  checks that the value in a field is a valid boolean value.
  If the value is boolean value, the boolean equivalent will be
  stored in the content hash. Otherwise, the default value for
  this field will be stored in the content hash instead.
  @param fieldDefinition The field_definition for this field.
  @param fieldName The name of the current field