Node version (or tell us if you're using electron or some other framework):

v6.2.1

ShellJS version (the most recent version/Github branch you see the bug on):

0.7.7

Operating system:

MacOS X 10.10

Description of the bug:

Occasionally, the exec command returns null instead of something valid. I have an automated build script that executes. Some time during the execution of the script, it fails with the error:

.../scripts/DocParser.js:51
		if (output.code === 0) {
		          ^

TypeError: Cannot read property 'code' of null

Example ShellJS command to reproduce the error:

const output = shelljs.exec(cmd, {silent: true});

These execs are called in a loop and it's not the first one that fails. If I call the script outside of the automation procedure, it runs to completion without issue. I'm super stumped on this one and could use any help debugging the problem.