Jenkinsfile / Pipeline DSL Groovy check if string is null or empty

Jenkinsfile.snippet1

def isStringBlankOrNull(s) {
    if ( s == null ) {
        return true
    } else if ( 0 == s.compareTo("") ) {
        return true
    }
    return false
}

stage('some stage') {
  node() {
    _null = null
    blank = ""
    names_list  = [ "null", "''", "\"\"", "\"\${blank}\"", "\"\${''}\"", "'string single quote'", "\"string double quote\"", "/regular expression/", "\"\${_null}\"", ]
    values_list = [  null,   '',    "",      "${blank}",   "${''}",       'string single quote',    "string double quote",    /regular expression/,     "${_null}",   ]
    for (int i = 0; i < names_list.size(); i++ ) {
      name  = names_list[i]
      value = values_list[i]
      _isStringBlankOrNull = isStringBlankOrNull(value)
      n = ( value == null ) ? true : false
      try {
        c = value.class
      } catch( e ) {
        c = ""
      }
      try {
        blank_cmp = value.compareTo("")
      } catch( e ) {
        blank_cmp = ""
      }
      echo "${i}: name {${name}} => value {${value}} (Is null: ${n}; class '${c}'; compare to blank: '${blank_cmp}'; isStringBlankOrNull '${_isStringBlankOrNull}')."
    }
  }
}

// OUTPUT:

// [Pipeline] echo
// 0: name {null} => value {null} (Is null: true; class ''; compare to blank: ''; isStringBlankOrNull 'true').
// [Pipeline] echo
// 1: name {''} => value {} (Is null: false; class 'class java.lang.String'; compare to blank: '0'; isStringBlankOrNull 'true').
// [Pipeline] echo
// 2: name {""} => value {} (Is null: false; class 'class java.lang.String'; compare to blank: '0'; isStringBlankOrNull 'true').
// [Pipeline] echo
// 3: name {"${blank}"} => value {} (Is null: false; class 'class org.codehaus.groovy.runtime.GStringImpl'; compare to blank: '0'; isStringBlankOrNull 'true').
// [Pipeline] echo
// 4: name {"${''}"} => value {} (Is null: false; class 'class org.codehaus.groovy.runtime.GStringImpl'; compare to blank: '0'; isStringBlankOrNull 'true').
// [Pipeline] echo
// 5: name {'string single quote'} => value {string single quote} (Is null: false; class 'class java.lang.String'; compare to blank: '19'; isStringBlankOrNull 'false').
// [Pipeline] echo
// 6: name {"string double quote"} => value {string double quote} (Is null: false; class 'class java.lang.String'; compare to blank: '19'; isStringBlankOrNull 'false').
// [Pipeline] echo
// 7: name {/regular expression/} => value {regular expression} (Is null: false; class 'class java.lang.String'; compare to blank: '18'; isStringBlankOrNull 'false').
// [Pipeline] echo
// 8: name {"${_null}"} => value {null} (Is null: false; class 'class org.codehaus.groovy.runtime.GStringImpl'; compare to blank: '4'; isStringBlankOrNull 'false').

//