code: public static String prependIfMissing(final String str, final CharSequence prefix, final CharSequence... prefixes) {
          return prependIfMissing(str, prefix, false, prefixes);
      }
docs: Prepends the prefix to the start of the string if the string does not
  already start with any of the prefixes.
  
  <pre>
  StringUtils.prependIfMissing(null, null) = null
  StringUtils.prependIfMissing("abc", null) = "abc"
  StringUtils.prependIfMissing("", "xyz") = "xyz"
  StringUtils.prependIfMissing("abc", "xyz") = "xyzabc"
  StringUtils.prependIfMissing("xyzabc", "xyz") = "xyzabc"
  StringUtils.prependIfMissing("XYZabc", "xyz") = "xyzXYZabc"
  </pre>
  <p>With additional prefixes,</p>
  <pre>
  StringUtils.prependIfMissing(null, null, null) = null
  StringUtils.prependIfMissing("abc", null, null) = "abc"
  StringUtils.prependIfMissing("", "xyz", null) = "xyz"
  StringUtils.prependIfMissing("abc", "xyz", new CharSequence[]{null}) = "xyzabc"
  StringUtils.prependIfMissing("abc", "xyz", "") = "abc"
  StringUtils.prependIfMissing("abc", "xyz", "mno") = "xyzabc"
  StringUtils.prependIfMissing("xyzabc", "xyz", "mno") = "xyzabc"
  StringUtils.prependIfMissing("mnoabc", "xyz", "mno") = "mnoabc"
  StringUtils.prependIfMissing("XYZabc", "xyz", "mno") = "xyzXYZabc"
  StringUtils.prependIfMissing("MNOabc", "xyz", "mno") = "xyzMNOabc"
  </pre>
  
  @param str The string.
  @param prefix The prefix to prepend to the start of the string.
  @param prefixes Additional prefixes that are valid.
  
  @return A new String if prefix was prepended, the same string otherwise.
  
  @since 3.2