$not on empty sequence should return empty sequence, like other functions

Signed-off-by: andrew-coleman <andrew_coleman@uk.ibm.com>

Author: andrew-coleman

src/functions.js

@@ -1433,6 +1433,11 @@ const functions = (() => {
      * @returns {boolean} - NOT arg
      */
     function not(arg) {
+        // undefined inputs always return undefined
+        if (typeof arg === 'undefined') {
+            return undefined;
+        }
+
         return !boolean(arg);
     }
 

test/test-suite/groups/boolean-expresssions/case027.json

@@ -0,0 +1,6 @@
+{
+    "expr": "$not(nothing)",
+    "data": {},
+    "bindings": {},
+    "undefinedResult": true
+}

test/test-suite/groups/function-signatures/case001.json

@@ -2,5 +2,5 @@
     "expr": "λ($arg)<b:b>{$not($arg)}(foo)",
     "dataset": null,
     "bindings": {},
-    "result": true
-}
+    "undefinedResult": true
+}