How do I Use Graphql Plugin to query where "fieldname != null"

I’m using Strapi 3.3.4 and strapi-plugin-graphql 3.3.4 at the moment and I am trying to query for records where a particular field is not null. I see in the graphql plugin docs under the section “Filters” and under the “where” subsection the last item in the unordered list says this:

  • <field>_null: Equals null/Not equals null

but when I use this where clause it does not filter out the records where the field does indeed have a null value:

where:{fieldname_null:false}

Oh yeah, and I’m using a mongo database.
Anyone know what I’m doing wrong?