Fix serialization issue for 0n. (yahoo#156)

Fix yahoo#125
Fix yahoo#154

Author: momocow

index.js

@@ -83,7 +83,7 @@ module.exports = function serialize(obj, options) {
             deleteFunctions(value);
         }
 
-        if (!value && value !== undefined) {
+        if (!value && value !== undefined && value !== BigInt(0)) {
             return value;
         }
 

test/unit/serialize.js

@@ -441,6 +441,12 @@ describe('serialize( obj )', function () {
             expect(serialize({t: [b]})).to.be.a('string').equal('{"t":[BigInt("9999")]}');
         });
 
+        it('should serialize 0n', function () {
+            var b = BigInt(0);
+            expect(serialize(b)).to.equal('BigInt("0")');
+            expect(serialize({t: [b]})).to.be.a('string').equal('{"t":[BigInt("0")]}');
+        });
+
         it('should deserialize BigInt', function () {
             var d = eval(serialize(BigInt(9999)));
             expect(d).to.be.a('BigInt');