public static String lowerCase(String str, Locale locale) {
        if (str == null) {
            return null;
        }
        return str.toLowerCase(locale);
    }
<p>Converts a String to lower case as per {@link String#toLowerCase(Locale)}.</p>

<p>A {@code null} input String returns {@code null}.</p>

<pre>
StringUtils.lowerCase(null, Locale.ENGLISH)  = null
StringUtils.lowerCase("", Locale.ENGLISH)    = ""
StringUtils.lowerCase("aBc", Locale.ENGLISH) = "abc"
</pre>

@param str  the String to lower case, may be null
@param locale  the locale that defines the case transformation rules, must not be null
@return the lower cased String, {@code null} if null String input
@since 2.5
android/android_framework/base/src/main/java/lang3/StringUtils.java