PhantomJS error "0 [ '' ]"

[nbyrd]

I have inherited a legacy ExtJS application that uses grunt-sencha-dependencies version 1.0.0 to install the sencha dependencies. In the Gruntfile, the following is defined:

sencha_dependencies: {
            legacy: {
                options: {
                    appJs: 'app.js',
                    senchaDir: 'extjs',
                    pageRoot: './client',
                    pageToProcess: 'dashboarddev.html',
                    includeAllScriptTags: false,
                    exclude: [
                        // These files will be included in the vendor bundle below.
                        // they are partially customized, so we cannot just pull latest vendor lib.
                        'client/mlpi/shared/videojs/video.js',
                        'client/mlpi/shared/videojs-extended.js',
                    ],
                },
            },
        },

When I run grunt, I get the following errors for the sencha_dependencies:legacy step.

Running "sencha_dependencies:legacy" (sencha_dependencies) task
Verifying property sencha_dependencies.legacy exists in config...OK
File: [no files]
Options: pageRoot="./client", includeAllScriptTags=false, failOnError=false, appJs="app.js", senchaDir="extjs", pageToProcess="dashboarddev.html", exclude=["client/mlpi/shared/videojs/video.js","client/mlpi/shared/videojs-extended.js"]
Processing Sencha app file dashboarddev.html...
Reading ./client/dashboarddev.html...OK
Processing source...OK
Writing ./client/766522.html...OK
Running PhantomJS...ERROR
>> 0 [ '' ]
Warning: PhantomJS exited unexpectedly with exit code null. Used --force, continuing.
Deleting ./client/766522.html...OK
>> TypeError: Cannot read property 'length' of null
Deleting ./client/766522.html...ERROR
>> Cannot delete nonexistent file.
✨  Done in 0.68s.

Can you clarify what this error means and how to address it?