First operand in a binary 'If' expression must be nullable or a reference type
An If expression can take either two or three arguments. When you send only two arguments, the first argument must be a reference type or a nullable type. If the first argument evaluates to anything other than Nothing, its value is returned. If the first argument evaluates to Nothing, the second argument is evaluated and returned.
For example, the following code contains two If expressions, one with three arguments and one with two arguments. The expressions calculate and return the same value.
' firstChoice is a nullable value type.
Dim firstChoice? As Integer = Nothing
Dim secondChoice As Integer = 1128
' If expression with three arguments.
Console.WriteLine(If(firstChoice IsNot Nothing, firstChoice, secondChoice))
' If expression with two arguments.
Console.WriteLine(If(firstChoice, secondChoice))
The following expressions cause this error:
Dim choice1 = 4
Dim choice2 = 5
Dim booleanVar = True
' Not valid.
'Console.WriteLine(If(choice1 < choice2, 1))
' Not valid.
'Console.WriteLine(If(booleanVar, "Test returns True."))
Error ID: BC33107
To correct this error
If you cannot change the code so that the first argument is a nullable type or reference type, consider converting to a three-argument If expression, or to an If...Then...Else statement.
Console.WriteLine(If(choice1 < choice2, 1, 2)) Console.WriteLine(If(booleanVar, "Test returns True.", "Test returns False."))