Why fruitless foreach returns N lines ?

Question

Hi, 
 I'm trying to test a fruitless foreach, and I'm surprised to see that the result is not just null or empty. - can you tell me why this code returns 20 null lines please (please see the attached file) ? I was expecting an empty list- 
 - In this case, how to assert that the result is fruitless ? 
 a!localVariables(
 /* Get a list of 20 Vehicles */
 local!vehicles: a!flatten(rule!CJT2_GetVehiclesWithFilters(
 id: null
 ).data),
 
 /* The id = 550 does not exist in the Vehicles so we'll not find it */
 local!oneVehicle: a!forEach(
 items: local!vehicles,
 expression: if(tointeger(fv!item.id)=550, 
 fv!item, 
 {}
 )
 ),
 
 local!oneVehicle
) 
 
 The object of this post, is not to replace foreach by another function (like index or reject) but to understand how works the foreach. 
 Regards

Richard Michaelis · Answer

to reduce it to the core: {} =-> List of variant with 0 items . You exuted it 20 times so you get a list of variant with 20 items and each of them are a list of variants with no element. The moment you have no other element, its ignored and for example a car cdt structure is shown a!isNullOrEmpty(local!oneVehicle) is still true This should solve your issue. local!oneVehicle: a!flatten(
 a!forEach(
 items: local!vehicles,
 expression: if(
 tointeger(fv!item.id)=550, 
 fv!item, 
 {}
 )
 )
 ),

Why fruitless foreach returns N lines ?

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