code: public static String stripToEmpty(final String str) {
          return N.isNullOrEmpty(str) ? N.EMPTY_STRING : strip(str, null);
      }
docs: <p>
  Strips whitespace from the start and end of a String returning an empty
  String if {@code null} input.
  </p>
  
  <p>
  This is similar to {@link #trimToEmpty(String)} but removes whitespace.
  Whitespace is defined by {@link Character#isWhitespace(char)}.
  </p>
  
  <pre>
  N.stripToEmpty(null)     = ""
  N.stripToEmpty("")       = ""
  N.stripToEmpty("   ")    = ""
  N.stripToEmpty("abc")    = "abc"
  N.stripToEmpty("  abc")  = "abc"
  N.stripToEmpty("abc  ")  = "abc"
  N.stripToEmpty(" abc ")  = "abc"
  N.stripToEmpty(" ab c ") = "ab c"
  </pre>
  
  @param str
  the String to be stripped, may be null
  @return the trimmed String, or an empty String if {@code null} input
  @since 2.0