invalid expression for if condition for Null value

[43918084]

I have below script that has no problem but ecounter Invalid expression once I add null condition.

Would appreciate experte guidance to make the correction.  Many thanks.

No issue in below script

load Distinct
key,
sum(timeSpentSeconds) as timeSpentSeconds,

if((sum([timeSpentSeconds])/60/60/8)>1,round(sum([timeSpentSeconds])/60/60/8)&'d', frAC(sum([timeSpentSeconds])/60/60/8)*8&'h')as [timeSpent_day_logged]
resident Worklog
group by key;

Drop table Worklog;

Invalid expression in below script

load Distinct
key,
sum(timeSpentSeconds) as timeSpentSeconds,

if(isnull([timeSpentSeconds]),'not specified',(if((sum([timeSpentSeconds])/60/60/8)>1,round(sum([timeSpentSeconds])/60/60/8)&'d', frAC(sum([timeSpentSeconds])/60/60/8)*8&'h')))

as [timeSpent_day_logged]
resident Worklog
group by key;

Drop table Worklog;

[marcus_sommer]

You may try:

load Key, coalesce(Expr, 'default) as Value from X group by Key;

[pravinboniface]

Can you share some data?  This is what I am using and it works for me.

Worklog:
load 
1 as key, Null() as timeSpentSeconds
AutoGenerate(1);
load 
2 as key, 100 as timeSpentSeconds
AutoGenerate(1);

newtab:
NoConcatenate
load Distinct
key,
sum(timeSpentSeconds) as timeSpentSeconds,

if(count([timeSpentSeconds])=0,'not specified',
	(if((sum([timeSpentSeconds])/60/60/8)>1,round(sum([timeSpentSeconds])/60/60/8)&'d', frAC(sum([timeSpentSeconds])/60/60/8)*8&'h')))

as [timeSpent_day_logged]

resident Worklog
group by key;

Drop table Worklog;

exit Script;

[43918084 · Accepted solution]

 Thank a lot to all experts for giving me many solutions.  After many trial and check, I have found that the "-" is because my table was joining another table and some of the value do not exist in the other table

So I use applymap instead and fix the problem.  

Regardless, Thank you so much for your guidance.  I have learned a lot more through the discussion.