code: public static String strip(String str, final String stripChars) {
          if (isEmpty(str)) {
              return str;
          }
          str = stripStart(str, stripChars);
          return stripEnd(str, stripChars);
      }
docs: <p>Strips any of a set of characters from the start and end of a String.
  This is similar to {@link String#trim()} but allows the characters
  to be stripped to be controlled.</p>
  
  <p>A {@code null} input String returns {@code null}.
  An empty string ("") input returns the empty string.</p>
  
  <p>If the stripChars String is {@code null}, whitespace is
  stripped as defined by {@link CharUtils#isWhitespace(char)}.
  Alternatively use {@link #strip(String)}.</p>
  
  <pre>
  StringUtils.strip(null, *)          = null
  StringUtils.strip("", *)            = ""
  StringUtils.strip("abc", null)      = "abc"
  StringUtils.strip("  abc", null)    = "abc"
  StringUtils.strip("abc  ", null)    = "abc"
  StringUtils.strip(" abc ", null)    = "abc"
  StringUtils.strip("  abcyx", "xyz") = "  abc"
  </pre>
  
  @param str  the String to remove characters from, may be null
  @param stripChars  the characters to remove, null treated as whitespace
  @return the stripped String, {@code null} if null String input