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