Web and SMTP api have optional callbacks.

In case you don't care about the callback for `send` or `smtp`,
it is now optional to supply a callback function.

lib/sendgrid.js

@@ -27,9 +27,11 @@ function SendGrid(api_user, api_key) {
  * @param  {Email|Object}  email     An email object or a hash that has
  *                                   the values for the email to be sent.
  * @param  {Function}      callback  A function to call when the processing is done.
+ *                                   This parameter is optional.
  */
 SendGrid.prototype.send = function(email, callback) {
-  var self = this;
+  var self = this
+    , cb = callback || function() { };
 
   var boundary = Math.random();
 
@@ -71,7 +73,7 @@ SendGrid.prototype.send = function(email, callback) {
       });
       res.on('end', function() {
         var json = JSON.parse(content);
-        callback(json.message == 'success', json.errors);
+        cb(json.message == 'success', json.errors);
       });
     });
 
@@ -93,7 +95,7 @@ SendGrid.prototype.send = function(email, callback) {
       if (success) {
         send_rest();
       } else {
-        callback(false, message);
+        cb(false, message);
       }
     });
   } else {
@@ -108,10 +110,12 @@ SendGrid.prototype.send = function(email, callback) {
  * @param    {Email|Object}  email     An email object or a hash that has
  *                                     the values for the email to be sent.
  * @param    {Function}      callback  A function to call when the processing is done.
+ *                                     This parameter is optional.
  */
 SendGrid.prototype.smtp = function(email, callback) {
   var self = this
-    , smtpTransport;
+    , smtpTransport
+    , cb = callback || function() { };
 
   // SMTP settings
   smtpTransport = nodemailer.createTransport("SMTP", {
@@ -126,9 +130,9 @@ SendGrid.prototype.smtp = function(email, callback) {
     smtpTransport.sendMail(email.toSmtpFormat(), function(error, response) {
       smtpTransport.close();
       if(error) {
-        return callback(false, response);
+        return cb(false, response);
       }
-      return callback(true, response);
+      return cb(true, response);
     });
   }
 
@@ -141,7 +145,7 @@ SendGrid.prototype.smtp = function(email, callback) {
       if (success) {
         send_smtp();
       } else {
-        callback(false, message);
+        cb(false, message);
       }
     });
   } else {

test/integration/sendgrid.test.js

@@ -136,6 +136,16 @@ describe('SendGrid', function () {
         done();
       });
     });
+
+    it('has an optional callback', function(done) {
+      var mail = new Email(text_params)
+
+      expect(function() {
+        sendgrid.send(mail);
+      }).to.not.throw(Error);
+
+      done();
+    });
   });
 
   describe('Smtp Api', function() {
@@ -220,6 +230,16 @@ describe('SendGrid', function () {
         done();
       });
     });
+
+    it('has an optional callback', function(done) {
+      var mail = new Email(text_params)
+
+      expect(function() {
+        sendgrid.smtp(mail);
+      }).to.not.throw(Error);
+
+      done();
+    });
   });
 
   describe('x-smtpapi', function(done) {