not able to select multiple options from the drop down

 Hello [mention:ffba947918f44b98ae5abe7badb7e8fc:e9ed411860ed4f2ba0265705b8793d05] ,

Is your variable/rule/expression configuration that you are using in the a!save() of your button widget to save the multiple data configured as an array type? 

Duplicate thread Please follow up in the current thread.

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Also you are trying to perform some updates in your button widget using ERs what exactly are you doing?

I feel like you're doing something funny with your local variable.  How is it initially declared / what is its initial value?  Why the a!defaultValue() wrapper?  And why, for a variable that inherently must be a list type, are you making it default to a single-type "null()"?  It seems like you should be defaulting it to an empty set ({}), if anything.