title: serial.println(String) prints "#" instead of the string
body: <p>i'm just trying to recieve a string using a serial and to send this string back. So when i send a string to an arduino over a serial the arduino should automaticly send this string back.</p>
  
  <p>i created this code:</p>
  
  <pre><code>String test;
  
  void setup(){
    Serial.begin(9600);
    Serial.setTimeout(2);
    test = "null";
  }
  
  void loop(){
    if(Serial.available()){
      test = Serial.readString();
    }
    Serial.println(test);
  }
  </code></pre>
  
  <p>I guess it is not that difficult to understand. However now the arduino will always print a "#" instead of the variable test. My connected serial device is a bluetooth modul. (hc-06)</p>
  
  <p>What did i do wrong?</p>
  
  <p>Thank you!</p>
  
  <p>(i also ran this code in the arduino emulator 123D Circuits. There it worked just fine)</p>