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Tools to assist in the reading of configuration/preferences files in various formats

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/*
 * 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.commons.configuration2.interpol;

/**
 * 
 * A simple dummy {@code Lookup} implementation.
 * 
 * 
 * This implementation always returns null for a passed in variable indicating that it cannot resolve that
 * variable. This is useful for instance as an application of the null object pattern.
 * 
 * 
 * This class does not define any state, therefore a single instance can be shared. To enforce usage of only a single
 * instance this class is actually an enumeration.
 * 
 *
 * @since 2.0
 */
public enum DummyLookup implements Lookup {
    /** The single instance of this class. */
    INSTANCE;

    /**
     * {@inheritDoc} This implementation always returns null.
     */
    @Override
    public Object lookup(final String variable) {
        return null;
    }
}