GeneratorAPI injectImports() function won't inject imports in an empty file.

[ericfennis]

Version

3.1.1

Reproduction link

https://github.com/ericfennis/vue-cli-iniectImport-bug

Node and OS info

node 8.12.0 / yarn 1.10.1 / MAC OSX Mojave

Steps to reproduce

1. Clone Repo

2. yarn to install dependecies

3. vue invoke bug

4. watch in cli:
   ERROR TypeError: Cannot convert undefined or null to object
   TypeError: Cannot convert undefined or null to object...

5. See location of the code in generator.js on line 15 in ./vue-cli-plugin-inject-bug/generator.js

What is expected?

Run vue invoke and the function inject the import in the empty file.

What is actually happening?

Gives error Object is null/undefined.

ERROR TypeError: Cannot convert undefined or null to object
TypeError: Cannot convert undefined or null to object
at injectImportsAndOptions (/Users/ericfennis/.config/yarn/global/node_modules/@vue/cli/lib/util/injectImportsAndOptions.js:28:28)
at Object.keys.forEach.file (/Users/ericfennis/.config/yarn/global/node_modules/@vue/cli/lib/Generator.js:211:21)
at Array.forEach ()
at Generator.resolveFiles (/Users/ericfennis/.config/yarn/global/node_modules/@vue/cli/lib/Generator.js:210:24)
at Generator.generate (/Users/ericfennis/.config/yarn/global/node_modules/@vue/cli/lib/Generator.js:116:16)
at runGenerator (/Users/ericfennis/.config/yarn/global/node_modules/@vue/cli/lib/invoke.js:121:19)
at
at process._tickCallback (internal/process/next_tick.js:189:7)

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I try to make a generator for a project and I want to inject importers in an empty file to register to export default them.