/*
 * The MIT License
 *
 * Copyright 2013 Oleg Nenashev <nenashev@synopsys.com>, Synopsys Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package com.synopsys.arc.jenkins.plugins.ownership.nodes;

import com.synopsys.arc.jenkins.plugins.ownership.OwnershipDescription;
import com.synopsys.arc.jenkins.plugins.ownership.util.AbstractOwnershipHelper;
import hudson.model.Computer;
import hudson.model.Node;
import hudson.model.User;
import java.io.IOException;
import java.util.Collection;

/**
 * Provides ownership helper for {@link Computer}.
 * The class implements a wrapper of {@link NodeOwnerHelper}.
 * @author Oleg Nenashev <nenashev@synopsys.com>, Synopsys Inc.
 */
public class ComputerOwnerHelper extends AbstractOwnershipHelper<Computer> {

    static final ComputerOwnerHelper Instance = new ComputerOwnerHelper();

    public static ComputerOwnerHelper getInstance() {
        return Instance;
    }
        
    @Override
    public OwnershipDescription getOwnershipDescription(Computer item) {
        Node node = item.getNode();      
        return node != null 
                ? NodeOwnerHelper.Instance.getOwnershipDescription(node)
                : OwnershipDescription.DISABLED_DESCR; // No node - no ownership
    }
    
    @Override
    public Collection<User> getPossibleOwners(Computer computer) {
        Node node = computer.getNode();
        return node != null 
                ? NodeOwnerHelper.Instance.getPossibleOwners(node)
                : EMPTY_USERS_COLLECTION;
    }  
    
    public static void setOwnership(Computer computer, OwnershipDescription descr) throws IOException {
        Node node = computer.getNode();
        if (node == null) {
            throw new IOException("Cannot set ownership. Probably, the node has been renamed or deleted.");
        }
        NodeOwnerHelper.setOwnership(computer.getNode(), descr);
    }
}

/*
 * The MIT License
 *
 * Copyright 2013 Oleg Nenashev <nenashev@synopsys.com>, Synopsys Inc.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package com.synopsys.arc.jenkins.plugins.ownership.nodes;

import com.synopsys.arc.jenkins.plugins.ownership.OwnershipDescription;
import com.synopsys.arc.jenkins.plugins.ownership.util.AbstractOwnershipHelper;
import hudson.model.Computer;
import hudson.model.Node;
import hudson.model.User;
import java.io.IOException;
import java.util.Collection;

/**
 * Provides ownership helper for {@link Computer}.
 * The class implements a wrapper of {@link NodeOwnerHelper}.
 * @author Oleg Nenashev <nenashev@synopsys.com>, Synopsys Inc.
 */
public class ComputerOwnerHelper extends AbstractOwnershipHelper<Computer> {

    static final ComputerOwnerHelper Instance = new ComputerOwnerHelper();

    public static ComputerOwnerHelper getInstance() {
        return Instance;
    }
        
    @Override
    public OwnershipDescription getOwnershipDescription(Computer item) {
        Node node = item.getNode();      
        return node != null 
                ? NodeOwnerHelper.Instance.getOwnershipDescription(node)
                : OwnershipDescription.DISABLED_DESCR; // No node - no ownership
    }
    
    @Override
    public Collection<User> getPossibleOwners(Computer computer) {
        Node node = computer.getNode();
        return node != null 
                ? NodeOwnerHelper.Instance.getPossibleOwners(node)
                : EMPTY_USERS_COLLECTION;
    }  
    
    public static void setOwnership(Computer computer, OwnershipDescription descr) throws IOException {
        Node node = computer.getNode();
        if (node == null) {
            throw new IOException("Cannot set ownership. Probably, the node has been renamed or deleted.");
        }
        
        ComputerOwnerHelper.setOwnership(computer, descr);
    }
}

Use a proper helper to avoid node deletion issues. Related to https://issues.jenkins-ci.org/browse/JENKINS-20488