more robust validation of createTx params

lib/server.js

@@ -1645,6 +1645,8 @@ WalletService.prototype._canCreateTx = function(cb) {
 WalletService.prototype._validateOutputs = function(opts, wallet, cb) {
   var dustThreshold = Math.max(Defaults.MIN_OUTPUT_AMOUNT, Bitcore.Transaction.DUST_AMOUNT);
 
+  if (_.isEmpty(opts.outputs)) return new ClientError('No outputs were specified');
+
   for (var i = 0; i < opts.outputs.length; i++) {
     var output = opts.outputs[i];
     output.valid = false;
@@ -1753,8 +1755,6 @@ WalletService.prototype.createTx = function(opts, cb) {
 
   opts = opts || {};
 
-  if (!checkRequired(opts, ['outputs'], cb)) return;
-
   function getChangeAddress(wallet, cb) {
     if (wallet.singleAddress) {
       self.storage.fetchAddresses(self.walletId, function(err, addresses) {

test/integration/server.js

@@ -2294,17 +2294,16 @@ describe('Wallet service', function() {
           });
         });
       });
-      it('should fail to create a tx without outputs param', function(done) {
+      it('should fail to create a tx without outputs', function(done) {
         helpers.stubUtxos(server, wallet, [1, 2], function() {
           var txOpts = {
-            toAddress: '18PzpUFkFZE8zKWUPvfykkTxmB9oMR8qP7',
-            amount: 0.8 * 1e8,
-            message: 'some message',
+            outputs: [],
             feePerKb: 123e2,
           };
           server.createTx(txOpts, function(err, tx) {
             should.exist(err);
             should.not.exist(tx);
+            err.message.should.equal('No outputs were specified');
             done();
           });
         });