How to check if integer comes null/empty : I need to check if an input comes null/empty.

    If input <= 100 And input > 0 And Not input = "" Then

       subjectsInt.Add(subjects(i), input)
	   check = True

    End If

I know in that code I am checking it as String but I already did `Not input = Nothing` and `Not input = 0` and I am getting an error:

>Run-time exception (line -1): Conversion from string "" to type 'Integer' is not valid.

>Stack Trace:

>[System.FormatException: Input string was not in a correct format.]

>[System.InvalidCastException: Conversion from string "" to type 'Integer' is not valid.]

Any suggestions?