Fix null handling.

- Updated handling of edge case null values due to previous changes.

Author: davidlehn

lib/expand.js

@@ -671,7 +671,7 @@ async function _expandObject({
             return ve;
           }
           return v;
-        }).filter(v => v !== null),
+        }),
         {propertyIsArray: options.isFrame});
       continue;
     }
@@ -1155,7 +1155,6 @@ function _expandValue({activeCtx, activeProperty, value, options}) {
           options
         });
       }
-      return {};
     }
     return {'@id': expandedValue};
   }

tests/misc.js

@@ -1203,6 +1203,7 @@ describe('events', () => {
       const expected =
 [
   {
+    "@id": null,
     "ex:p": [
       {
         "@value": "v"
@@ -1240,7 +1241,11 @@ describe('events', () => {
       const expected =
 [
   {
-    "ex:idp": [{}],
+    "ex:idp": [
+      {
+        "@id": null
+      }
+    ],
     "ex:p": [
       {
         "@value": "v"
@@ -1278,6 +1283,7 @@ describe('events', () => {
       const expected =
 [
   {
+    "@id": null,
     "ex:p": [
       {
         "@value": "v"
@@ -1315,7 +1321,11 @@ describe('events', () => {
       const expected =
 [
   {
-    "ex:idp": [{}],
+    "ex:idp": [
+      {
+        "@id": null
+      }
+    ],
     "ex:p": [
       {
         "@value": "v"