/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache license, Version 2.0
 * (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.apache.org/licenses/LICENSE-2.0
 *
 * 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.apache.logging.log4j.core.appender;

import java.io.Serializable;
import java.util.Objects;

import javax.script.Bindings;

import org.apache.logging.log4j.core.Appender;
import org.apache.logging.log4j.core.Filter;
import org.apache.logging.log4j.core.Layout;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginBuilderAttribute;
import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
import org.apache.logging.log4j.core.config.plugins.PluginElement;
import org.apache.logging.log4j.core.config.plugins.validation.constraints.Required;
import org.apache.logging.log4j.core.script.AbstractScript;
import org.apache.logging.log4j.core.script.ScriptManager;

@Plugin(name = "ScriptAppenderSelector", category = "Core", elementType = "appender", printObject = true)
public class ScriptAppenderSelector extends AbstractAppender {

    /**
     * Builds an appender.
     */
    public static final class Builder implements org.apache.logging.log4j.core.util.Builder<Appender> {

        @PluginElement("AppenderSet")
        @Required
        private AppenderSet appenderSet;

        @PluginConfiguration
        @Required
        private Configuration configuration;

        @PluginBuilderAttribute
        @Required
        private String name;

        @PluginElement("Script")
        @Required
        private AbstractScript script;

        @Override
        public Appender build() {
            if (name == null) {
                LOGGER.error("Name missing.");
            }
            if (script == null) {
                LOGGER.error("Script missing for ScriptAppenderSelector appender {}", name);
            }
            if (appenderSet == null) {
                LOGGER.error("AppenderSet missing for ScriptAppenderSelector appender {}", name);
            }
            if (configuration == null) {
                LOGGER.error("Configuration missing for ScriptAppenderSelector appender {}", name);
            }
            final ScriptManager scriptManager = configuration.getScriptManager();
            scriptManager.addScript(script);
            final Bindings bindings = scriptManager.createBindings(script);
            final Object object = scriptManager.execute(script.getName(), bindings);
            final String appenderName = Objects.toString(object, null);
            final Appender appender = appenderSet.createAppender(appenderName, name);
            return appender;
        }

        public AppenderSet getAppenderSet() {
            return appenderSet;
        }

        public Configuration getConfiguration() {
            return configuration;
        }

        public String getName() {
            return name;
        }

        public AbstractScript getScript() {
            return script;
        }

        public Builder withAppenderNodeSet(@SuppressWarnings("hiding") final AppenderSet appenderSet) {
            this.appenderSet = appenderSet;
            return this;
        }

        public Builder withConfiguration(@SuppressWarnings("hiding") final Configuration configuration) {
            this.configuration = configuration;
            return this;
        }

        public Builder withName(@SuppressWarnings("hiding") final String name) {
            this.name = name;
            return this;
        }

        public Builder withScript(@SuppressWarnings("hiding") final AbstractScript script) {
            this.script = script;
            return this;
        }

    }

    @PluginBuilderFactory
    public static Builder newBuilder() {
        return new Builder();
    }

    private ScriptAppenderSelector(final String name, final Filter filter, final Layout<? extends Serializable> layout) {
        super(name, filter, layout);
    }

    @Override
    public void append(final LogEvent event) {
        // Do nothing: This appender is only used to discover and build another appender
    }

}

@@ -2539,16 +2539,45 @@
 ing.%22);%0A
+                return null;%0A
         
@@ -2574,32 +2574,32 @@
 ;%0A            %7D%0A
-
             if (
@@ -2701,32 +2701,61 @@
 der %7B%7D%22, name);%0A
+                return null;%0A
             %7D%0A  
@@ -2881,32 +2881,61 @@
 der %7B%7D%22, name);%0A
+                return null;%0A
             %7D%0A  
@@ -2965,32 +2965,32 @@
 tion == null) %7B%0A
-
                 
@@ -3065,32 +3065,61 @@
 der %7B%7D%22, name);%0A
+                return null;%0A
             %7D%0A  

Fix NPEs.