fix #67

avoid tupleBindings to be empty

Author: aeberhart

src/main/java/com/dashjoin/jsonata/Jsonata.java

@@ -432,7 +432,7 @@ Frame createFrameFromTuple(Frame environment, Map<String, Object> tuple) {
         ((JList)result).tupleStream = true;
         var stepEnv = environment;
         if(tupleBindings == null) {
-            tupleBindings = (List<Map>) input.stream().filter(item -> item!=null).map(item -> Map.of("@", item)).collect(Collectors.toList());
+            tupleBindings = (List<Map>) input.stream().map(item -> Utils.mapOf("@", item)).collect(Collectors.toList());
         }
 
         for(var ee = 0; ee < tupleBindings.size(); ee++) {

src/main/java/com/dashjoin/jsonata/Utils.java

@@ -20,6 +20,7 @@
 import java.util.AbstractList;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
@@ -268,5 +269,14 @@ public static void quote(String string, StringBuilder w) {
               }
           }
       }
-  }
+    }
+
+    /**
+     * version of Map.of(key, value) that allows value to be null
+     */
+    static Map mapOf(String key, Object value) {
+        Map<String, Object> map = new HashMap<>();
+        map.put(key, value);
+        return map;
+    }
 }

src/test/java/com/dashjoin/jsonata/ArrayTest.java

@@ -29,7 +29,6 @@ public void filterTest() {
     Assertions.assertNotNull(expr.evaluate(Map.of("variable", Map.of("field", "1"))));
   }
 
-  @Disabled
   @Test
   public void testIndex() {
     Jsonata expr = jsonata("($x:=['a','b']; $x#$i.$i)");