fix error when inserting an invalid document

Author: ecarriou

src/db.js

@@ -715,8 +715,11 @@ DatabaseCollection.prototype.insert = function insert(document) {
       var component = null;
       var channels = [];
       var channel = null;
-
+       
       switch (true) {
+        case obj === null: 
+          $log.invalidDocumentOnDbInsert(obj, this.name);
+          break;
         case this.name === '_Schema':
         case this.name === '_Logger':
         case this.name === '_Model':

test/module/db-spec.js

@@ -157,6 +157,11 @@ describe('System Runtime db component', () => {
 
     expect(docAdded[0]).equal('runtime1');
 
+    // try to insert an invalid document
+    let invalidDoc = db._Runtime.insert(null);
+    
+    expect(invalidDoc.length).equal(0);
+
     // try to insert the same document
     docAdded = db._Runtime.insert({
       '_id': 'runtime1',