fix(merkling): Fix saving of objects with null properties

fix #1

src/ipld.js

@@ -62,11 +62,11 @@ class IpldProxy {
   }
 
   isIpld (obj) {
-    return this.allowedStatuses.includes(obj[statusSymbol])
+    return obj && this.allowedStatuses.includes(obj[statusSymbol])
   }
 
   isPersisted (obj) {
-    return obj[statusSymbol] === this.UNLOADED || obj[statusSymbol] === this.SAVED
+    return obj && (obj[statusSymbol] === this.UNLOADED || obj[statusSymbol] === this.SAVED)
   }
 
   create (cid, status, obj) {

src/merkling.js

@@ -75,13 +75,15 @@ const Merkling = function (options) {
         return resolve(elem)
       }
 
-      const subpersists = Object.keys(elem).map(key => {
-        return typeof elem[key] === 'object'
-          ? this._persist(elem[key])
-          : null
-      }).filter(Boolean)
-
-      return Promise.all(subpersists).then((values) => {
+      const subpersists = Object.keys(elem)
+        .filter(key => elem[key])
+        .map(key => {
+          return typeof elem[key] === 'object'
+            ? this._persist(elem[key])
+            : null
+        }).filter(Boolean)
+
+      return Promise.all(subpersists).then(() => {
         if (!this.ipldProxy.isIpld(elem)) {
           return resolve(elem)
         }
@@ -102,6 +104,10 @@ const Merkling = function (options) {
   }
 
   this._substituteMerkleLinks = (elem) => {
+    if (!elem) {
+      return elem
+    }
+
     const dagNode = this.ipldProxy.extract(elem)
 
     Object.keys(dagNode).forEach(key => {

test/merkling.test.js

@@ -85,6 +85,18 @@ describe('api tests', () => {
     done()
   })
 
+  test('Save an object with a nested null', async (done) => {
+    const simple = { name: 'Example', next: null }
+    const node = merkle.create(simple)
+    const savedNode = await merkle.save(node)
+    expect(savedNode).not.toBeNull()
+    expect(savedNode.name).toBe('Example')
+    expect(savedNode._cid).not.toBeNull()
+    expect(savedNode._cid.toBaseEncodedString()).toBe('zdpuAm1ZHnidGxaUbTExkEeEYZRG6jxNPsgeZNe53L6hB5Ny6')
+    expect(savedNode.next).toBeNull()
+    done()
+  })
+
   test('Saving null throws', () => {
     expect(() => { merkle.save(null) }).toThrow('Argument exception, trying to save null or undefined')
   })