Allow null as a filter value

[jingsam]

mapbox-gl-js: 0.33.1
When I tried to filter out null values like this:

filter: [
  "!=",
  "name",
  null
]

But it warns:

string, number, or boolean expected, null found

[mourner]

You can do this currently with ['has', 'name'] filter. However we might want to support null as a valid value too. Did we consider this @jfirebaugh?

[jfirebaugh]

Yes, see mapbox/mapbox-gl-style-spec#421. Main reason we haven't implemented it is in most cases you want ['has', 'name'], not ["!=", "name", null], because vector tiles don't support null (mapbox/vector-tile-spec#62).

[jingsam]

But geojson does suuport null

[stevage]

What would the semantics of has be for a null value then? Does a feature has a value, if that value is null? And is it really useful to be able to distinguish "", null and not-present?

[lucaswoj]

@stevage I spent some time thinking about this while implementing mapbox/mapbox-gl-style-spec#451. My conclusion was that we should be as true to the Javascript semantics as possible. This would suggest that we should support null in Map#setFilter. (undefined is a sticker case because it isn't supported in JSON.)

[stevage]

Ah, thanks for pointing me to that.

[zuo1188]

so it's awkward

[zuo1188]

or please do not render it when property==null

[benstadin]

@zuo1188 I can top this! ;)

To me this is an important feature for data-driven styling. Because you get GeoJSON data often from external data sources, and null is a valid value.

I think an isNUll comparator would be handy.

[anandthakker]

Closing this, as it will be covered by the upcoming 'arbitrary expressions' feature #4777

[qrohlf]

Correct me if I'm wrong, but after reading this, #421, and #4777, it appears that the intent in these discussions was to support a filter like ["==", "temp", null] for asserting that a feature has the property temp and it is equal to null, but the actual functionality doesn't appear to have made it into the product. As far as I can tell, map.setFilter("mylayer", ["==", "temp", null]) is currently a no-op and does not result in any filtering being applied to my data.

[Dimi4ek]

I think has using when we need to check existing field in properties.
Can we use filter: ['to-boolean', ['get', 'fieldName']] ??