code: public static int indexOf(String str, String searchStr) {
        if (str == null || searchStr == null) {
            return -1;
        }
        return str.indexOf(searchStr);
    }
docs: <p>Finds the first index within a String, handling <code>null</code>.
  This method uses {@link String#indexOf(String)}.</p>
  
  <p>A <code>null</code> String will return <code>-1</code>.</p>
  
  <pre>
  GosuStringUtil.indexOf(null, *)          = -1
  GosuStringUtil.indexOf(*, null)          = -1
  GosuStringUtil.indexOf("", "")           = 0
  GosuStringUtil.indexOf("aabaabaa", "a")  = 0
  GosuStringUtil.indexOf("aabaabaa", "b")  = 2
  GosuStringUtil.indexOf("aabaabaa", "ab") = 1
  GosuStringUtil.indexOf("aabaabaa", "")   = 0
  </pre>
  
  @param str  the String to check, may be null
  @param searchStr  the String to find, may be null
  @return the first index of the search String,
  -1 if no match or <code>null</code> string input
  @since 2.0