I have hundreds of XLS files that need to be aggregated, but I find that each file has more or less missing values or error messages. Is there any way to quickly clean up these missing values or error messages? Because I still don't know how to clean up a lot of data, so the following code only extract the data in different files.

(*   Get a list of files   *)
dir = "D:\\Data";
fileList = FileNames["*", dir];
For[i = 1, i = Length[fileList], i++,
 If[i == 1,
      rawdata = Import[fileList[[i]], {"XLS", "Data"}][[1]];    (*i=1 olny *)
     ,
  {
   tempData = Rest@Import[fileList[[i]], {"XLS", "Data"}][[1]];        (*i != 1*)
   rawdata = AppendTo[rawdata, tempData];
   }
  ]
 ]