Conditionally include a property

[Michele Bartolucci (mickybar)]

I have a case where I want to conditionally omit a property for a resource.

I'd like to have that property set to false in certain conditions, but the property does not accept it. If it's present it needs to be true. If I want to set it to false, it has to be omitted altogether.

I am aware we can conditionally set a value for a property, but that does not apply in this case.

Is there a way to do this in bicep (or ARM)?

[Alex Frankel (alex-frankel)]

Have you tried setting the value to null when the condition is false? This typically gets handled by the resource as if the property was not declared.

[Michele Bartolucci (mickybar)]

Hi Alex,
brilliant, I didn't think about it. It worked

[Justin Grote (JustinGrote)]

Michele Bartolucci (@mickybar) a lot of the tricks in ARM still work here, for instance using json('null') for complex object properties, or just '' for strings.

See my fortigate templte for a lot of example of conditional properties and settings/"knobs"
https://github.com/justingrote/fortigateazureha

[Marcin Jastrzebski (majastrz)]

JSON now supports the null() function that should be used instead of json('null'). In bicep, the equivalent is the null keyword.

[Justin Grote (JustinGrote)]

I've tried it but have still had issues when supplying partial objects to configs like virtualmachines, and had to resort to json('null'), especially with conditionals.

EDIT: here's an example where only json('null') works. I forgot to show it here but null() isn't even a recognized bicep expression

Capture.mp4

[Marcin Jastrzebski (majastrz)]

This is a bug in the type system. (null returns a value of type null and json('...') returns a value of any type, which is assignable to all types.) Can you open an issue for it and include the mp4?

The workaround that should work is any(null) in Bicep until we fix it.

[Michele Bartolucci (mickybar)]

Thanks everyone for the suggestions. In my case I just needed a boolean value and using null in bicep made the trick

[GraceLewis45]

Seeing the loading error on the Azure/Bicep thread reminded me how fragile the preview pane can be when testing conditional property inclusions, nested modules expecting a fully resolved object. In practice, treating the template like a well‑structured dataset—much like consulting Dade property data for accurate cross‑references—helps you validate defaults before the deployment engine evaluates them. If the page still won’t render, a hard refresh or clearing the cache usually forces the Bicep compiler to reload the latest JSON, letting you verify the conditional logic now resolves without errors.

[racheladams12]

I noticed the page repeatedly throws the “error while loading” message, which usually means the Bicep compiler didn’t receive the full JSON payload. In those cases I treat the problem like I would when validating Wakulla property values verify the source data before the engine processes it. Reloading the file, clearing the browser cache, and running az bicep build with the --no-restore flag normally resolves the conditional property inclusion glitch.