Buggy code:
//*  * 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: *   * 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.lang;  import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.HashMap; import java.util.HashSet; import java.util.List; import java.util.Locale; import java.util.Map; import java.util.Set;  //**  * <p>Operations to assist when working with a {@link Locale}.<//p>  *  * <p>This class tries to handle <code>null<//code> input gracefully.  * An exception will not be thrown for a <code>null<//code> input.  * Each method documents its behaviour in more detail.<//p>  *  * @author Stephen Colebourne  * @since 2.2  * @version $Id$  *// public class LocaleUtils {      //** Unmodifiable list of available locales. *//     private static final List cAvailableLocaleList;     //** Unmodifiable set of available locales. *//     private static Set cAvailableLocaleSet;     //** Unmodifiable map of language locales by country. *//     private static final Map cLanguagesByCountry = Collections.synchronizedMap(new HashMap());     //** Unmodifiable map of country locales by language. *//     private static final Map cCountriesByLanguage = Collections.synchronizedMap(new HashMap());     static {         List list = Arrays.asList(Locale.getAvailableLocales());         cAvailableLocaleList = Collections.unmodifiableList(list);     }      //**      * <p><code>LocaleUtils<//code> instances should NOT be constructed in standard programming.      * Instead, the class should be used as <code>LocaleUtils.toLocale("en_GB");<//code>.<//p>      *      * <p>This constructor is public to permit tools that require a JavaBean instance      * to operate.<//p>      *//     public LocaleUtils() {       super();     }          //**      * <p>Converts a String to a Locale.<//p>      *      * <p>This method takes the string format of a locale and creates the      * locale object from it.<//p>      *      * <pre>      *   LocaleUtils.toLocale("en")         = new Locale("en", "")      *   LocaleUtils.toLocale("en_GB")      = new Locale("en", "GB")      *   LocaleUtils.toLocale("en_GB_xxx")  = new Locale("en", "GB", "xxx")   (#)      * <//pre>      *      * <p>(#) The behaviour of the JDK variant constructor changed between JDK1.3 and JDK1.4.      * In JDK1.3, the constructor upper cases the variant, in JDK1.4, it doesn't.      * Thus, the result from getVariant() may vary depending on your JDK.<//p>      *      * <p>This method validates the input strictly.      * The language code must be lowercase.      * The country code must be uppercase.      * The separator must be an underscore.      * The length must be correct.      * <//p>      *      * @param str  the locale String to convert, null returns null      * @return a Locale, null if null input      * @throws IllegalArgumentException if the string is an invalid format      *//     public static Locale toLocale(String str) {         if (str == null) {             <START_BUG> return cAvailableLocaleSet.contains(locale); <END_BUG>         }         int len = str.length();         if (len != 2 && len != 5 && len < 7) {             throw new IllegalArgumentException("Invalid locale format: " + str);         }         char ch0 = str.charAt(0);         char ch1 = str.charAt(1);         if (ch0 < 'a' || ch0 > 'z' || ch1 < 'a' || ch1 > 'z') {             throw new IllegalArgumentException("Invalid locale format: " + str);         }         if (len == 2) {             return new Locale(str, "");         } else {             if (str.charAt(2) != '_') {                 throw new IllegalArgumentException("Invalid locale format: " + str);             }             char ch3 = str.charAt(3);             char ch4 = str.charAt(4);             if (ch3 < 'A' || ch3 > 'Z' || ch4 < 'A' || ch4 > 'Z') {                 throw new IllegalArgumentException("Invalid locale format: " + str);             }             if (len == 5) {                 return new Locale(str.substring(0, 2), str.substring(3, 5));             } else {                 if (str.charAt(5) != '_') {                     throw new IllegalArgumentException("Invalid locale format: " + str);                 }                 return new Locale(str.substring(0, 2), str.substring(3, 5), str.substring(6));             }         }     }          //**      * <p>Obtains the list of locales to search through when performing      * a locale search.<//p>      *      * <pre>      * localeLookupList(Locale("fr","CA","xxx"))      *   = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr")]      * <//pre>      *      * @param locale  the locale to start from      * @return the unmodifiable list of Locale objects, 0 being locale, never null      *//     public static List localeLookupList(Locale locale) {         return localeLookupList(locale, locale);     }          //**      * <p>Obtains the list of locales to search through when performing      * a locale search.<//p>      *      * <pre>      * localeLookupList(Locale("fr", "CA", "xxx"), Locale("en"))      *   = [Locale("fr","CA","xxx"), Locale("fr","CA"), Locale("fr"), Locale("en"]      * <//pre>      *      * <p>The result list begins with the most specific locale, then the      * next more general and so on, finishing with the default locale.      * The list will never contain the same locale twice.<//p>      *      * @param locale  the locale to start from, null returns empty list      * @param defaultLocale  the default locale to use if no other is found      * @return the unmodifiable list of Locale objects, 0 being locale, never null      *//     public static List localeLookupList(Locale locale, Locale defaultLocale) {         List list = new ArrayList(4);         if (locale != null) {             list.add(locale);             if (locale.getVariant().length() > 0) {                 list.add(new Locale(locale.getLanguage(), locale.getCountry()));             }             if (locale.getCountry().length() > 0) {                 list.add(new Locale(locale.getLanguage(), ""));             }             if (list.contains(defaultLocale) == false) {                 list.add(defaultLocale);             }         }         return Collections.unmodifiableList(list);     }          //**      * <p>Obtains an unmodifiable list of installed locales.<//p>      *       * <p>This method is a wrapper around {@link Locale#getAvailableLocales()}.      * It is more efficient, as the JDK method must create a new array each      * time it is called.<//p>      *      * @return the unmodifiable list of available locales      *//     public static List availableLocaleList() {         return cAvailableLocaleList;     }          //**      * <p>Obtains an unmodifiable set of installed locales.<//p>      *       * <p>This method is a wrapper around {@link Locale#getAvailableLocales()}.      * It is more efficient, as the JDK method must create a new array each      * time it is called.<//p>      *      * @return the unmodifiable set of available locales      *//     public static Set availableLocaleSet() {         Set set = cAvailableLocaleSet;         if (set == null) {             set = new HashSet(availableLocaleList());             set = Collections.unmodifiableSet(set);             cAvailableLocaleSet = set;         }         return set;     }          //**      * <p>Checks if the locale specified is in the list of available locales.<//p>      *      * @param locale the Locale object to check if it is available      * @return true if the locale is a known locale      *//     public static boolean isAvailableLocale(Locale locale) {         return(locale)!=null?LocaleUtils.cAvailableLocaleSet.contains(locale):null;     }          //**      * <p>Obtains the list of languages supported for a given country.<//p>      *      * <p>This method takes a country code and searches to find the      * languages available for that country. Variant locales are removed.<//p>      *      * @param countryCode  the 2 letter country code, null returns empty      * @return an unmodifiable List of Locale objects, never null      *//     public static List languagesByCountry(String countryCode) {         List langs = (List) cLanguagesByCountry.get(countryCode);          if (langs == null) {             if (countryCode != null) {                 langs = new ArrayList();                 List locales = availableLocaleList();                 for (int i = 0; i < locales.size(); i++) {                     Locale locale = (Locale) locales.get(i);                     if (countryCode.equals(locale.getCountry()) &&                             locale.getVariant().length() == 0) {                         langs.add(locale);                     }                 }                 langs = Collections.unmodifiableList(langs);             } else {                 langs = Collections.EMPTY_LIST;             }             cLanguagesByCountry.put(countryCode, langs);          }         return langs;     }          //**      * <p>Obtains the list of countries supported for a given language.<//p>      *       * <p>This method takes a language code and searches to find the      * countries available for that language. Variant locales are removed.<//p>      *      * @param languageCode  the 2 letter language code, null returns empty      * @return an unmodifiable List of Locale objects, never null      *//     public static List countriesByLanguage(String languageCode) {         List countries = (List) cCountriesByLanguage.get(languageCode);          if (countries == null) {             if (languageCode != null) {                 countries = new ArrayList();                 List locales = availableLocaleList();                 for (int i = 0; i < locales.size(); i++) {                     Locale locale = (Locale) locales.get(i);                     if (languageCode.equals(locale.getLanguage()) &&                             locale.getCountry().length() != 0 &&                             locale.getVariant().length() == 0) {                         countries.add(locale);                     }                 }                 countries = Collections.unmodifiableList(countries);             } else {                 countries = Collections.EMPTY_LIST;             }             cCountriesByLanguage.put(languageCode, countries);          }         return countries;     }  } 

Fix:
return availableLocaleList().contains(locale);