stream: objectMode transforms allow falsey values

Closes #6183

lib/_stream_transform.js

@@ -174,7 +174,7 @@ Transform.prototype._write = function(chunk, encoding, cb) {
 Transform.prototype._read = function(n) {
   var ts = this._transformState;
 
-  if (ts.writechunk && ts.writecb && !ts.transforming) {
+  if (ts.writechunk !== null && ts.writecb && !ts.transforming) {
     ts.transforming = true;
     this._transform(ts.writechunk, ts.writeencoding, ts.afterTransform);
   } else {

test/simple/test-stream-transform-objectmode-falsey-value.js

@@ -0,0 +1,53 @@
+// Copyright Joyent, Inc. and other Node contributors.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a
+// copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to permit
+// persons to whom the Software is furnished to do so, subject to the
+// following conditions:
+//
+// The above copyright notice and this permission notice shall be included
+// in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN
+// NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
+// DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
+// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE
+// USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+var common = require('../common');
+var assert = require('assert');
+
+var stream = require('stream');
+var PassThrough = stream.PassThrough;
+
+var src = new PassThrough({ objectMode: true });
+var tx = new PassThrough({ objectMode: true });
+var dest = new PassThrough({ objectMode: true });
+
+var expect = [ -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ];
+var results = [];
+process.on('exit', function() {
+  assert.deepEqual(results, expect);
+  console.log('ok');
+});
+
+dest.on('data', function(x) {
+  results.push(x);
+});
+
+src.pipe(tx).pipe(dest);
+
+var i = -1;
+var int = setInterval(function() {
+  if (i > 10) {
+    src.end();
+    clearInterval(int);
+  } else {
+    src.write(i++);
+  }
+});