Problem when files haven't any result

[jsaintvanne]

When files haven't any results between them, we have an error when we try to run sweep function :

Error in FUN(x, aperm(array(STATS, dims[perm]), order(perm)), ...) : 
  non-numeric argument to binary operator
Calls: runGC -> sweep```

[jsaintvanne]

Should be corrected here yguitton/metaMS#14

[jsaintvanne]

After discussion, I should modify that because when a file has no results matching it is not an error it is a result NULL...
So I should modify the error as a NULL result !