Reverting part of PR #4286

This is because it trips up the Closure compiler with errors like:

ERROR - assignment to property bb of SomeTable
found : undefined
required: (flatbuffers.ByteBuffer|null)
this.bb = undefined;
^^^^^^^^^^^^^^^^^^^

Change-Id: Iaf032b5249ec655e151331e81532e549c12bcd78

src/idl_gen_js.cpp

@@ -593,7 +593,7 @@ void GenStruct(const Parser &parser, StructDef &struct_def,
     code += "  /**\n";
     code += "   * @type {flatbuffers.ByteBuffer}\n";
     code += "   */\n";
-    code += "  this.bb = undefined;\n";
+    code += "  this.bb = null;\n";
     code += "\n";
     code += "  /**\n";
     code += "   * @type {number}\n";

tests/monster_test_generated.js

@@ -50,7 +50,7 @@ MyGame.Example2.Monster = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}
@@ -101,7 +101,7 @@ MyGame.Example.Test = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}
@@ -185,7 +185,7 @@ MyGame.Example.TestSimpleTableWithEnum = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}
@@ -267,7 +267,7 @@ MyGame.Example.Vec3 = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}
@@ -439,7 +439,7 @@ MyGame.Example.Ability = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}
@@ -522,7 +522,7 @@ MyGame.Example.Stat = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}
@@ -654,7 +654,7 @@ MyGame.Example.Monster = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}

tests/namespace_test/namespace_test1_generated.js

@@ -28,7 +28,7 @@ NamespaceA.NamespaceB.TableInNestedNS = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}
@@ -110,7 +110,7 @@ NamespaceA.NamespaceB.StructInNestedNS = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}

tests/namespace_test/namespace_test2_generated.js

@@ -25,7 +25,7 @@ NamespaceA.TableInFirstNS = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}
@@ -141,7 +141,7 @@ NamespaceC.TableInC = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}
@@ -226,7 +226,7 @@ NamespaceA.SecondTableInA = function() {
   /**
    * @type {flatbuffers.ByteBuffer}
    */
-  this.bb = undefined;
+  this.bb = null;
 
   /**
    * @type {number}