/*

  * Copyright 2011 The Kuali Foundation

  *

  * Licensed under the Educational Community License, Version 1.0 (the "License");

  * you may not use this file except in compliance with the License.

  * You may obtain a copy of the License at

  *

  * http://www.opensource.org/licenses/ecl1.php

  *

  * Unless required by applicable law or agreed to in writing, software

  * distributed under the License is distributed on an "AS IS" BASIS,

  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

  * See the License for the specific language governing permissions and

  * limitations under the License.

  */

 package org.kuali.rice.core.api.criteria;

 import javax.xml.bind.annotation.XmlAccessType;

 import javax.xml.bind.annotation.XmlAccessorType;

 import javax.xml.bind.annotation.XmlAttribute;

 import javax.xml.bind.annotation.XmlRootElement;

 import javax.xml.bind.annotation.XmlType;

 import org.apache.commons.lang.StringUtils;

 /**

  * An immutable expression which represents an "is null" statement which is

  * evaluated the property defined by the property path on this expression.

  * 

  * <p>Constructed as part of a {@link Criteria} when built using a

  * {@link CriteriaBuilder}.

  * 

  * @see Criteria

  * @see CriteriaBuilder

  * 

  * @author Kuali Rice Team (rice.collab@kuali.org)

  *

  */

 @XmlRootElement(name = NullExpression.Constants.ROOT_ELEMENT_NAME)

 @XmlAccessorType(XmlAccessType.NONE)

 @XmlType(name = NullExpression.Constants.TYPE_NAME)

 public final class NullExpression extends AbstractExpression implements PropertyPathExpression {

         private static final long serialVersionUID = 2397296074921454859L;

         @XmlAttribute(name = CriteriaSupportUtils.PropertyConstants.PROPERTY_PATH)

         private final String propertyPath;

         /**

      * Should only be invoked by JAXB.

      */

     @SuppressWarnings("unused")

     private NullExpression() {

         this.propertyPath = null;

     }

     /**

          * Constructs a NullExpression for the given propertyPath.

          * 

          * @param propertyPath the property path for the expression, must not be null or blank

          * 

          * @throws IllegalArgumentException if the propertyPath is null or blank

          */

     NullExpression(String propertyPath) {

             if (StringUtils.isBlank(propertyPath)) {

                         throw new IllegalArgumentException("Property path cannot be null or blank.");

                 }

                 this.propertyPath = propertyPath;

     }

     @Override

     public String getPropertyPath() {

             return propertyPath;

     }

         /**

      * Defines some internal constants used on this class.

      */

     static class Constants {

         final static String ROOT_ELEMENT_NAME = "null";

         final static String TYPE_NAME = "NullType";

     }

 }