fix: handle null/undefined as last query value in mysql and postgres …

…patchers (#81)

* fix: handle null/undefined as last query value

Was beforehand throwing a TypeError when trying to access the constructor property on `null` or `undefined`:

```js
connection.query('SELECT a FROM b', null);
// without xray --> resolves query
// with xray    --> throws TypeError: Cannot read property 'constructor' of null  
```

As far as I know null and undefined are the only data types that will encounter this problem, hence a loose null check should suffice.

* fix: handle null/undefined as last query value in postgres

* test: add test cases for sending null in last query parameter

packages/mysql/lib/mysql_p.js

@@ -92,7 +92,7 @@ function resolveArguments(argsObj) {
       args.callback = typeof argsObj[1] === 'function' ? argsObj[1] : (typeof argsObj[2] === 'function' ? argsObj[2] : undefined);
     }
 
-    args.segment = (argsObj[argsObj.length-1].constructor && (argsObj[argsObj.length-1].constructor.name === 'Segment' ||
+    args.segment = (argsObj[argsObj.length-1] != null && argsObj[argsObj.length-1].constructor && (argsObj[argsObj.length-1].constructor.name === 'Segment' ||
       argsObj[argsObj.length-1].constructor.name === 'Subsegment')) ? argsObj[argsObj.length-1] : null;
   }
 

packages/mysql/test/unit/mysql_p.test.js

@@ -143,6 +143,12 @@ describe('captureMySQL', function() {
 
         stubClose.should.have.been.calledWithExactly(err);
       });
+
+      it('should start a new automatic context when last query paramater is null', function() {
+        query.call(connectionObj, 'sql here', function() {}, null);
+
+        assert.equal(stubBaseQuery.args[0][2].name, 'autoContext');
+      });
     });
   });
 

packages/postgres/lib/postgres_p.js

@@ -44,7 +44,7 @@ function resolveArguments(argsObj) {
       args.callback = typeof argsObj[1] === 'function' ? argsObj[1] : (typeof argsObj[2] === 'function' ? argsObj[2] : undefined);
     }
 
-    args.segment = (argsObj[argsObj.length-1].constructor && (argsObj[argsObj.length-1].constructor.name === 'Segment' ||
+    args.segment = (argsObj[argsObj.length-1] != null && argsObj[argsObj.length-1].constructor && (argsObj[argsObj.length-1].constructor.name === 'Segment' ||
       argsObj[argsObj.length-1].constructor.name === 'Subsegment')) ? argsObj[argsObj.length-1] : null;
   }
 

packages/postgres/test/unit/postgres_p.test.js

@@ -135,6 +135,12 @@ describe('capturePostgres', function() {
 
       stubClose.should.have.been.calledWithExactly(err);
     });
+
+    it('should start a new automatic context when last query paramater is null', function() {
+      query.call(postgres, 'sql here', [], function() {}, null);
+
+      assert.equal(queryObj.callback.name, 'autoContext');
+    });
   });