Fix to distinguish between NULL and empty string values.

Signed-off-by: Felix Geisendörfer <felix@debuggable.com>

lib/mysql/parser.js

@@ -494,7 +494,7 @@ Parser.prototype.write = function(buffer) {
 
         packet.columnLength = lengthCoded(packet.columnLength);
         if (!packet.columnLength) {
-          packet.emit('data', new Buffer(0), 0);
+          packet.emit('data', (packet.columnLength === null ? null : new Buffer(0)), 0);
           if (packet.received < packet.length) {
             advance(Parser.COLUMN_VALUE_LENGTH);
           } else {

lib/mysql/query.js

@@ -53,7 +53,7 @@ Query.prototype._handlePacket = function(packet) {
       row[field] = '';
 
       packet.on('data', function(buffer, remaining) {
-        if (buffer.length) {
+        if (buffer) {
           row[field] += buffer;
         } else {
           row[field] = null;

test/system/test-client-query-empty.js

@@ -0,0 +1,16 @@
+require('../common');
+var Client = require('mysql').Client,
+    client = Client(TEST_CONFIG),
+    gently = new Gently();
+
+// our test db might not exist yet, so don't try to connect to it
+client.database = '';
+client.connect();
+
+client.query('SELECT "" as field_a', function(err, results) {
+  if (err) throw err;
+
+  assert.strictEqual(results[0].field_a, "");
+  client.end();
+});
+