code: public static boolean contains(final CharSequence seq, final int searchChar) {
          if (isEmpty(seq)) {
              return false;
          }
          return CharSequenceUtils.indexOf(seq, searchChar, 0) >= 0;
      }
docs: <p>Checks if CharSequence contains a search character, handling {@code null}.
  This method uses {@link String#indexOf(int)} if possible.</p>
  
  <p>A {@code null} or empty ("") CharSequence will return {@code false}.</p>
  
  <pre>
  StringUtils.contains(null, *)    = false
  StringUtils.contains("", *)      = false
  StringUtils.contains("abc", 'a') = true
  StringUtils.contains("abc", 'z') = false
  </pre>
  
  @param seq  the CharSequence to check, may be null
  @param searchChar  the character to find
  @return true if the CharSequence contains the search character,
  false if not or {@code null} string input
  @since 2.0
  @since 3.0 Changed signature from contains(String, int) to contains(CharSequence, int)