handle 0 input txs

lib/server.js

@@ -1207,6 +1207,9 @@ WalletService.prototype.getSendMaxInfo = function(opts, cb) {
 
         lastFee = fee;
       });
+
+      if (_.isEmpty(txp.inputs)) return cb(null, info);
+
       info.size = txp.getEstimatedSize();
       info.fee = txp.getEstimatedFee();
       info.amount = _.sum(txp.inputs, 'satoshis') - info.fee;

test/integration/server.js

@@ -3745,7 +3745,6 @@ describe('Wallet service', function() {
         });
       });
     });
-
     it('should exclude unconfirmed inputs', function(done) {
       helpers.stubUtxos(server, wallet, ['u0.1', 0.2, 0.3, 0.4], function() {
         server.getSendMaxInfo({
@@ -3817,6 +3816,22 @@ describe('Wallet service', function() {
         });
       });
     });
+    it('should work when all inputs are below their cost in fee', function(done) {
+      helpers.stubUtxos(server, wallet, ['u 10bit', '10bit', '20bit'], function() {
+        server.getSendMaxInfo({
+          feePerKb: 500e2,
+          returnInputs: true,
+        }, function(err, info) {
+          should.not.exist(err);
+          should.exist(info);
+          info.inputs.should.be.empty;
+          info.size.should.equal(0);
+          info.fee.should.equal(0);
+          info.amount.should.equal(0);
+          done();
+        });
+      });
+    });
     it('should not go beyond max tx size', function(done) {
       var _oldDefault = Defaults.MAX_TX_SIZE_IN_KB;
       Defaults.MAX_TX_SIZE_IN_KB = 2;