I thought that the first constraint on design would cause all to fail if null, but I'm getting results from the conde statement afterwards in my unit tests.

gistfile1.clj

; Logic Code
(defn uri-path [design view search path]                                                 
  (logic/!= nil design)                                                                  
  (logic/conde                                                                           
   [(logic/!= nil view) (logic/== ["_design" design "_view" view] path)]))

; Unit test
(test/deftest test-path
  (test/is (= '()
              (logic/run* [q] (db/uri-path nil "view" "search" q))))
  (test/is (= '(["_design" "design" "_view" "view"])
              (logic/run* [q] (db/uri-path "design" "view" nil q)))))

; Test results
; FAIL in (test-path) (db_test.clj:24)
; expected: (= (quote ()) (logic/run* [q] (db/uri-path nil "view" "search" q)))
  ; actual: (not (= () (["_design" nil "_view" "view"])))

; The solution
(defn uri-path [design view search path]
  (logic/fresh [x]
               (logic/== x design)
               (logic/!= x nil)
               (logic/conde
                [(logic/!= nil view) (logic/== ["_design" x "_view" view] path)])))