`node -e ''` should mean eval(''), not invoke REPL

Fixes #1116

src/node.js

@@ -75,7 +75,7 @@
       // Main entry point into most programs:
       process.nextTick(Module.runMain);
 
-    } else if (process._eval) {
+    } else if (process._eval != null) {
       // User passed '-e' or '--eval' arguments to Node.
       var Module = NativeModule.require('module');
       var rv = new Module()._compile('return eval(process._eval)', 'eval');

test/simple/test-cli-eval.js

@@ -47,3 +47,9 @@ child.exec(nodejs + ' --eval "require(\'./test/simple/test-cli-eval.js\')"',
     function(status, stdout, stderr) {
       assert.equal(status.code, 42);
     });
+
+// empty program should do nothing
+child.exec(nodejs + ' -e ""', function(status, stdout, stderr) {
+  assert.equal(stdout, 'undefined\n');
+  assert.equal(stderr, '');
+});