If condition with another condition inside the result part.

Hello, 

I am thinking how I can achieve something like this with seal only, 

a!localVariables(
local!data:
if(
isnull(local!a1),

updatedictionary(),
/* Second Condition */
if(isnull(local!b1),
),

),
null
),
local!data
)

basically if condition for null value, if it is null exit, if it is not null do action and that check next value, problem is that in the if there are condition, true(), false()) where it does not allows a action with another if inside the result part. 

Any idea which is the best approach ?