multiple classes (eg IDate is integer and IDate) results in warning for is.overlapping

[myoung3]

in is.overlapping

  if(class(start)!=class(end)){     stop("start and end must be of the same class")   }

will result in this warning

In if (class(start) != class(end)) { ... :
  the condition has length > 1 and only the first element will be used

if object has multiple classes