code: public static String toUpperCase(final String str, final Locale locale) {
          if (N.isNullOrEmpty(str)) {
              return str;
          }
  
          return str.toUpperCase(locale);
      }
docs: <p>
  Converts a String to upper case as per {@link String#toUpperCase(Locale)}
  .
  </p>
  
  <p>
  A {@code null} input String returns {@code null}.
  </p>
  
  <pre>
  N.toUpperCase(null, Locale.ENGLISH)  = null
  N.toUpperCase("", Locale.ENGLISH)    = ""
  N.toUpperCase("aBc", Locale.ENGLISH) = "ABC"
  </pre>
  
  @param str
  the String to upper case, may be null
  @param locale
  the locale that defines the case transformation rules, must
  not be null
  @return the upper cased String, {@code null} if null String input
  @since 2.5