code: public static String stripToEmpty(final String str) {
          return str == null ? EMPTY : 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 CharUtils#isWhitespace(char)}.</p>
  
  <pre>
  StringUtils.stripToEmpty(null)     = ""
  StringUtils.stripToEmpty("")       = ""
  StringUtils.stripToEmpty("   ")    = ""
  StringUtils.stripToEmpty("abc")    = "abc"
  StringUtils.stripToEmpty("  abc")  = "abc"
  StringUtils.stripToEmpty("abc  ")  = "abc"
  StringUtils.stripToEmpty(" abc ")  = "abc"
  StringUtils.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