Small fix

extron.py

@@ -41,7 +41,7 @@ class ExtronSerial(SerialDevice):
     def send_command(self, command: str) -> str:
         response = super().send_command(command)
 
-        if response[0] == "E":
+        if response and response[0] == "E":
             print(response, self.ERRORS.get(response, "Unknown"))
 
         return response

serialdevice.py

@@ -1,4 +1,4 @@
-from doctest import REPORT_CDIFF
+import sys
 from serial import Serial
 
 
@@ -27,7 +27,7 @@ class SerialDevice:
                 response = ""
 
             if not response:
-                print(self.prefix, "No response")
+                print(self.prefix, "No response:", command, file=sys.stderr)
             elif self.verbose:
                 print(self.prefix, "resp:", response)