In Lacinia, I have a query with an argument of type List without Non-Null type modifier. If I provide argument value null using a query variable I'll get nil from the resolver's argument map as I would have expected. However, if I provide null directly as a query argument value it seems to be coerced to an empty list. For example:

(require '[com.walmartlabs.lacinia.schema :as schema])
(require '[com.walmartlabs.lacinia :as lacinia])
(let [s (schema/compile {:queries {:testQuery {:type    '(list Int)
                                               :args    {:testArg {:type '(list Int)}}
                                               :resolve (fn [ctx args v]
                                                          (println "testArg =" (:testArg args))
                                                          (:testArg args))}}})
      with-variable "query ($testArg:[Int]) {
                         testQuery(testArg: $testArg)
                      }"
      without-variable "query {
                            testQuery(testArg: null)
                      }"      
      ]

  (println "with-variable =" (lacinia/execute s with-variable {:testArg nil} nil))
  (println "without-variable =" (lacinia/execute s without-variable nil nil)))

testArg = nil
with-variable = {:data #ordered/map ([:testQuery nil])}
testArg = []
without-variable = {:data #ordered/map ([:testQuery []])}