ruby - Can't use conditions on symbols. DataMapper with Sinatra -

i'm getting troubles when trying use conditions on symbols in datamapper:

 clusters = cluster.all(:latitude.not => nil) 

this code throws error:

argumenterror - condition #<origin::key:0x50d05a0 @name=:latitude, @strategy=:__override__, @operator="$not", @expanded=nil, @block= nil> of unsupported object origin::key:         c:/ruby21/lib/ruby/gems/2.1.0/gems/dm-core-1.2.1/lib/dm-core/query.rb:888:in `block in assert_valid_conditions'         c:/ruby21/lib/ruby/gems/2.1.0/gems/dm-core-1.2.1/lib/dm-core/query.rb:853:in `each'         c:/ruby21/lib/ruby/gems/2.1.0/gems/dm-core-1.2.1/lib/dm-core/query.rb:853:in `assert_valid_conditions'         c:/ruby21/lib/ruby/gems/2.1.0/gems/dm-core-1.2.1/lib/dm-core/query.rb:776:in `block in assert_valid_options'         c:/ruby21/lib/ruby/gems/2.1.0/gems/dm-core-1.2.1/lib/dm-core/query.rb:766:in `each'         c:/ruby21/lib/ruby/gems/2.1.0/gems/dm-core-1.2.1/lib/dm-core/query.rb:766:in `assert_valid_options'         c:/ruby21/lib/ruby/gems/2.1.0/gems/dm-core-1.2.1/lib/dm-core/query.rb:363:in `update'         c:/ruby21/lib/ruby/gems/2.1.0/gems/dm-core-1.2.1/lib/dm-core/query.rb:386:in `merge'         c:/ruby21/lib/ruby/gems/2.1.0/gems/dm-core-1.2.1/lib/dm-core/model.rb:767:in `scoped_query' 

cluster model class:

class cluster   include datamapper::resource    property :id,               serial   property :city_id,          integer   property :name,             string   property :latitude,         float   property :longitude,        float       end 

core gem versions i'm using: sinatra - 1.4.6, data_mapper - 1.2.0.

what can wrong code? can't resolve error.

you this:

clusters = cluster.all - cluster.all(:latitude => nil)  

reference (combining queries 13)