NullPointerException error with Nullable field

[Anonymous]

Hello,
I am faced with a 'java.lang.NullPointerException' when I set a null value in a (nullable) field. 
The error is just at the t_map, I am not yet inserting in a database.
Here is the transformation I am doing

Relational.ISNULL(StringHandling.TRIM(Stie_adresse.CANDIDAT_STATU)) ? null :
"Tim".equalsIgnoreCase(StringHandling.TRIM(Stie_adresse.CANDIDAT_STATU))? 1 :
"Sup".equalsIgnoreCase(StringHandling.TRIM(Stie_adresse.CANDIDAT_STATU))? 0 : null

When I replace null by 999 there is no error

Relational.ISNULL(StringHandling.TRIM(Stie_adresse.CANDIDAT_STATU)) ? 999 :
"Tim".equalsIgnoreCase(StringHandling.TRIM(Stie_adresse.CANDIDAT_STATU))? 1 :
"Sup".equalsIgnoreCase(StringHandling.TRIM(Stie_adresse.CANDIDAT_STATU))? 0 : 999

I don't understand why I am getting the error since my fields are nullabe.

Any help please? Thank you

[Anonymous]

Have you looked at the line that is throwing the exception in the Code view, to see exactly what is causing the exception?
As you suggest, everything here seems ok