code: public static String trimToEmpty(final String str) {
          return N.isNullOrEmpty(str) ? N.EMPTY_STRING : str.trim();
      }
docs: <p>
  Removes control characters (char &lt;= 32) from both ends of this String
  returning an empty String ("") if the String is empty ("") after the trim
  or if it is {@code null}.
  
  <p>
  The String is trimmed using {@link String#trim()}. Trim removes start and
  end characters &lt;= 32. To strip whitespace use
  {@link #stripToEmpty(String)}.
  </p>
  
  <pre>
  N.trimToEmpty(null)          = ""
  N.trimToEmpty("")            = ""
  N.trimToEmpty("     ")       = ""
  N.trimToEmpty("abc")         = "abc"
  N.trimToEmpty("    abc    ") = "abc"
  </pre>
  
  @param str
  the String to be trimmed, may be null
  @return the trimmed String, or an empty String if {@code null} input
  @since 2.0