sign_recoverable can raise a ValueError, handling it.

common/cryptographer.py

@@ -281,10 +281,15 @@ class Cryptographer:
             logger.error("The value passed as sk is not a private key (EllipticCurvePrivateKey)")
             return None
 
+        try:
             rsig_rid = sk.sign_recoverable(LN_MESSAGE_PREFIX + message, hasher=sha256d)
             sigrec = sigrec_encode(rsig_rid)
             zb32_sig = pyzbase32.encode_bytes(sigrec).decode()
 
+        except ValueError:
+            logger.error("Couldn't sign the message")
+            return None
+
         return zb32_sig
 
     @staticmethod