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Hibernate's core ORM functionality

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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or .
 */
package org.hibernate.query.criteria.internal.predicate;

import java.io.Serializable;
import javax.persistence.criteria.Expression;

import org.hibernate.query.criteria.internal.CriteriaBuilderImpl;
import org.hibernate.query.criteria.internal.ParameterRegistry;
import org.hibernate.query.criteria.internal.Renderable;
import org.hibernate.query.criteria.internal.compile.RenderingContext;
import org.hibernate.query.criteria.internal.expression.UnaryOperatorExpression;

/**
 * Defines a {@link javax.persistence.criteria.Predicate} for checking the
 * nullness state of an expression, aka an IS [NOT] NULL predicate.
 * 
 * The NOT NULL form can be built by calling the constructor and then
 * calling {@link #not}.
 *
 * @author Steve Ebersole
 */
public class NullnessPredicate
		extends AbstractSimplePredicate
		implements UnaryOperatorExpression, Serializable {
	private final Expression operand;

	/**
	 * Constructs the affirmitive form of nullness checking (IS NULL).  To
	 * construct the negative form (IS NOT NULL) call {@link #not} on the
	 * constructed instance.
	 *
	 * @param criteriaBuilder The query builder from whcih this originates.
	 * @param operand The expression to check.
	 */
	public NullnessPredicate(CriteriaBuilderImpl criteriaBuilder, Expression operand) {
		super( criteriaBuilder );
		this.operand = operand;
	}

	@Override
	public Expression getOperand() {
		return operand;
	}

	@Override
	public void registerParameters(ParameterRegistry registry) {
		Helper.possibleParameter( getOperand(), registry );
	}

	@Override
	public String render(boolean isNegated, RenderingContext renderingContext) {
		return ( (Renderable) operand ).render( renderingContext ) + check( isNegated );
	}

	private String check(boolean negated) {
		return negated ? " is not null" : " is null";
	}
}