Bug? If not recognizing null

[RVP]

I have the following test

        If (valSDate <> Null  AND valSDate <> "" AND valSDate.Length>0) Then
 
            dteScheduled.SetDate(DateTime.DateParse(valSDate),True)
        Else
            dteScheduled.SetDate(-1,True)
        End If

Per the debugger

valSDate
value = null

However the code still runs the first part of the if statement, instead of the else section

 

[Erel]

Where did this null came from?

When you compare a string variable with another object the other object is first converted to string. The result is that you are comparing the string with "null".

 

[RVP]

Similar to this

Dim myMap AsMap
 
    myMap.Initialize
    myMap = DBUtils.ExecuteMap(Main.SQL1,SQLScripts.LoadTimeDetail(rowId),Null)
 
Dim tmpstDate AsString : tmpstDate = myMap.Get("st")
Dim tmpetDate AsString : tmpetDate = myMap.Get("en")
 
If ( tmpstDate = Null OR tmpstDate = "" OR tmpstDate.Length=0) Then
    txtStartDate.SetDate(-1,True)
Else
    txtStartDate.SetDate(DateTime.DateParse(tmpstDate),True)
EndIf

How do I check for a null value then?

 

[Erel]

My previous answer was not correct.
The conversion happens here:

Dim t As String = Null

At this point the Null is converted to a string. t value is "null".
You can change your check to:

If tmpstDate = "null" OR ... Then
[/cod]e

 

[MaFu]

Similar to this

Dim myMap AsMap

    myMap.Initialize
    myMap = DBUtils.ExecuteMap(Main.SQL1,SQLScripts.LoadTimeDetail(rowId),Null)

Dim tmpstDate AsString : tmpstDate = myMap.Get("st")
Dim tmpetDate AsString : tmpetDate = myMap.Get("en")

If ( tmpstDate = Null OR tmpstDate = "" OR tmpstDate.Length=0) Then
    txtStartDate.SetDate(-1,True)
Else
    txtStartDate.SetDate(DateTime.DateParse(tmpstDate),True)
EndIf

How do I check for a null value then?

And another point:
if a string is empty then it's length is always 0, if a string is not empty the length cannot be 0.
Therefore it's no need for both checks (tmpstDate = "" OR tmpstDate.Length=0), you only need one.