correct some error

LINQJS.code-workspace

@@ -0,0 +1,8 @@
+{
+	"folders": [
+		{
+			"path": ".."
+		}
+	],
+	"settings": {}
+}

linq.js

@@ -1099,7 +1099,7 @@ Enumerable.prototype.leftJoin = function (inner, outerKeySelector, innerKeySelec
                         const key = outerKeySelector(outerEnumerator.current());
                         innerElements = lookup.get(key).toArray();
                         // execute once if innerElements is NULL
-                        if (innerElements == null) {
+                        if (innerElements == null || innerElements.length == 0) {
                             return this.yieldReturn(resultSelector(outerEnumerator.current(), null));
                         }
                     } else {

test/join.js

@@ -85,3 +85,27 @@ test("groupJoin", function ()
                 { outer: 6, collection: [2, 4, 6, 6]}];
     deepEqual(actual, expected);
 });
+
+test("leftJoin", function ()
+{
+    var math = { yamada: 100, tanaka: 80, yoshida: 94 };
+    var english = { yamada: 73, tanaka: 99 };
+    let actual = Enumerable.from(math)
+        .leftJoin(english, "outer=>outer.key", "inner=>inner.key",
+            (o,i) => ({Name:o.key,Math:o.value,English:i == null ? null : i.value}))
+        .toArray();
+    let expected = [{ Name: "yamada", Math: 100, English: 73 },
+                    { Name: "tanaka", Math: 80, English: 99 },
+                    { Name: "yoshida", Math: 94, English: null}];
+    deepEqual(actual, expected);
+
+    actual = Enumerable.from(math)
+        .leftJoin(english, "outer=>outer", "inner=>inner",
+        (o,i) => ({Name:o.key,Math:o.value,English:i == null ? null : i.value}), 
+        "$.key")
+        .toArray();
+    expected = [{ Name: "yamada", Math: 100, English: 73 },
+                { Name: "tanaka", Math: 80, English: 99 },
+                { Name: "yoshida", Math: 94, English: null}];
+    deepEqual(actual, expected);
+});