If-Condition with empty variable

Hey,

I do have measurements with an Measurment number, but some Measurement number do not exist.

For context, I have the following code. In general it works fine.

Dim SourceData = [IC_I_U_RMS, IHV_Sys_ave, MeasNr, Record]
Dim maxIHV, maxIC
Dim Idx, _Event, _Event2, maxMeasNr, Idx2
Dim Maxima, Idexes, baum
Dim startIdx, endIdx
maxMeasNr = Maximum(MeasNr.Y)


For i = 1 To maxMeasNr Do

_Event = ValuesInInterval(MeasNr, i, i, EVENT_INDEX)
_Event2 = ValuesInInterval(Record, 1, 1, EVENT_INDEX)
Idx = IndexAnd(_Event, _Event2)


If Idx = ???  Then
	maxIHV :="NaN"
	maxIC :="NaN"
Else
	startIdx = Minimum(Idx)
	endIdx = Maximum(Idx)
	maxIHV := Maximum(IHV_Sys_ave[startIdx, endIdx], )
	maxIC := Maximum(IC_I_U_RMS[startIdx, endIdx], )
End

Maxima = {maxIHV, maxIC}

End

My Problem is, that if “IndexAnd()” has no common indexes, it outputs an empty variable. This happens when the MeasNr doesnt exist. If the MeasNr doesnt exist the code is supposed to write down “NaN”. So if the variable Idx is empty the code should write “NaN” and if it isn`t empty it should write an value.

What i can`t figure out is how to write the “if var Idx equals empty then…” = If Idx = ?EMPTY? Then…

How can i solve this? I can`t put down: False, “”, 0 etc.

Thanks in advance!