Null cannot be used in property expressions on Android

[mjaakko]

Is your feature request related to a problem? Please describe.
Yes. I need to get the first non-null and non-empty string from a list of values to use localized labels on the map. Unfortunately in the data source I'm using, missing values can either be null or an empty string. coalesce operator could be used to get rid of nulls, but that won't for empty strings. case operator could be used to map empty strings to nulls, but it's not possible to use nulls in expressions

Describe the solution you'd like
Allow using nulls in expressions, e.g. Expression.null() or Expression.literal(null)

Describe alternatives you've considered
Using a nested case expression with all, has and != works in this case, but it becomes quite clunky with more complex conditions

Additional context
mjaakko/NeoStumbler#941

[louwers]

Sorry for the late reply.

I think this is a limitation of the MapLibre Style Spec. Could you open an issue here?

[TimSylvester]

@mjaakko have you tried something like ["==", ["typeof", ["get", "propertyName"]], "null"]?

I don't see any examples in our test cases, but it seems like it might work.

A quick test indicates that it works in the JS implementation, at least.

[mjaakko]

@louwers I think it should be supported by the spec already? https://maplibre.org/maplibre-style-spec/expressions/#expressions

Each argument is either a literal value (a string, number, boolean, or null), or another expression array.