code: public static int indexOf(final CharSequence seq, final int searchChar) {
          if (isEmpty(seq)) {
              return INDEX_NOT_FOUND;
          }
          return CharSequenceUtils.indexOf(seq, searchChar, 0);
      }
docs: Returns the index within <code>seq</code> of the first occurrence of
  the specified character. If a character with value
  <code>searchChar</code> occurs in the character sequence represented by
  <code>seq</code> <code>CharSequence</code> object, then the index (in Unicode
  code units) of the first such occurrence is returned. For
  values of <code>searchChar</code> in the range from 0 to 0xFFFF
  (inclusive), this is the smallest value <i>k</i> such that:
  <blockquote><pre>
  this.charAt(<i>k</i>) == searchChar
  </pre></blockquote>
  is true. For other values of <code>searchChar</code>, it is the
  smallest value <i>k</i> such that:
  <blockquote><pre>
  this.codePointAt(<i>k</i>) == searchChar
  </pre></blockquote>
  is true. In either case, if no such character occurs in <code>seq</code>,
  then {@code INDEX_NOT_FOUND (-1)} is returned.
  
  <p>Furthermore, a {@code null} or empty ("") CharSequence will
  return {@code INDEX_NOT_FOUND (-1)}.</p>
  
  <pre>
  StringUtils.indexOf(null, *)         = -1
  StringUtils.indexOf("", *)           = -1
  StringUtils.indexOf("aabaabaa", 'a') = 0
  StringUtils.indexOf("aabaabaa", 'b') = 2
  </pre>
  
  @param seq  the CharSequence to check, may be null
  @param searchChar  the character to find
  @return the first index of the search character,
  -1 if no match or {@code null} string input
  @since 2.0
  @since 3.0 Changed signature from indexOf(String, int) to indexOf(CharSequence, int)
  @since 3.6 Updated {@link CharSequenceUtils} call to behave more like <code>String</code>