mitigates unclear nimsuggest problem

compiler/transf.nim

@@ -304,6 +304,7 @@ proc transformYield(c: PTransf, n: PNode): PTransNode =
   var e = n.sons[0]
   # c.transCon.forStmt.len == 3 means that there is one for loop variable
   # and thus no tuple unpacking:
+  if e.typ.isNil: return result # can happen in nimsuggest for unknown reasons
   if skipTypes(e.typ, {tyGenericInst}).kind == tyTuple and
       c.transCon.forStmt.len != 3:
     e = skipConv(e)