don't await `nil` futures

ws/session.nim

@@ -93,7 +93,7 @@ proc send*(
   ws: WSSession,
   data: seq[byte] = @[],
   opcode: Opcode): Future[void]
-  {.raises: [Defect, WSClosedError].} =
+  {.async, raises: [Defect, WSClosedError].} =
   ## Send a frame
   ##
 
@@ -117,9 +117,12 @@ proc send*(
       default(MaskKey)
 
   if opcode in {Opcode.Text, Opcode.Cont, Opcode.Binary}:
-    return ws.writeMessage(data, opcode, maskKey, ws.extensions)
+    await ws.writeMessage(
+      data, opcode, maskKey, ws.extensions)
 
-  return ws.writeControl(data, opcode, maskKey)
+    return
+
+  await ws.writeControl(data, opcode, maskKey)
 
 proc send*(
   ws: WSSession,
@@ -389,7 +392,6 @@ proc recv*(
     if not ws.binary and validateUTF8(pbuffer.toOpenArray(0, consumed - 1)) == false:
       raise newException(WSInvalidUTF8, "Invalid UTF8 sequence detected")
 
-    return consumed
   except CatchableError as exc:
     trace "Exception reading frames", exc = exc.msg
     ws.readyState = ReadyState.Closed
@@ -402,6 +404,8 @@ proc recv*(
       trace "Last frame in message and no more bytes left to read, reseting current frame"
       ws.frame = nil
 
+  return consumed
+
 proc recv*(
   ws: WSSession,
   size = WSMaxMessageSize): Future[seq[byte]] {.async.} =