Build fails with `fingerprinting.prepend = true`

Fails in version `2.0.0`
This bug does not exist in `master`/`3.0.0`
The version shipped with latest `ember-cli: 3.8.1` is `2.0.0`
https://github.com/ef4/ember-auto-import/issues/94#issuecomment-469038012

```js
ENV Summary:

TIME: Sun Mar 03 2019 21:22:28 GMT+0530 (India Standard Time)
TITLE: ember
ARGV:
- /usr/local/Cellar/node@10/10.15.0/bin/node
- /usr/local/bin/ember
- s
EXEC_PATH: /usr/local/Cellar/node@10/10.15.0/bin/node
TMPDIR: /var/folders/gy/vrp1632j5432m8f64r1n_c6m0000gn/T
SHELL: /bin/bash
PATH:
- /usr/local/opt/node@10/bin
- /usr/local/bin
- /usr/local/bin
- /usr/bin
- /bin
- /usr/sbin
- /sbin
PLATFORM: darwin x64
FREEMEM: 3480100864
TOTALMEM: 8589934592
UPTIME: 24936
LOADAVG: 7.51513671875,4.2802734375,3.32666015625
CPUS:
- Intel(R) Core(TM) i5-3335S CPU @ 2.70GHz - 2700
- Intel(R) Core(TM) i5-3335S CPU @ 2.70GHz - 2700
- Intel(R) Core(TM) i5-3335S CPU @ 2.70GHz - 2700
- Intel(R) Core(TM) i5-3335S CPU @ 2.70GHz - 2700
ENDIANNESS: LE
VERSIONS:
- ares: 1.15.0
- cldr: 34.0
- http_parser: 2.8.0
- icu: 63.1
- modules: 64
- napi: 3
- nghttp2: 1.34.0
- node: 10.15.0
- openssl: 1.1.0j
- tz: 2018e
- unicode: 11.0
- uv: 1.23.2
- v8: 6.8.275.32-node.45
- zlib: 1.2.11

ERROR Summary:

- broccoliBuilderErrorStack: TypeError: Cannot read property '2' of null
at AssetRewrite.rewriteAssetPath (/Users/sumeet/projects/srp-client/node_modules/broccoli-asset-rewrite/index.js:127:91)
at AssetRewrite.processString (/Users/sumeet/projects/srp-client/node_modules/broccoli-asset-rewrite/index.js:167:24)
at AssetRewrite.processFile (/Users/sumeet/projects/srp-client/node_modules/broccoli-filter/index.js:165:31)
at asyncProcessFile (/Users/sumeet/projects/srp-client/node_modules/broccoli-filter/index.js:122:21)
at tryCatch (/Users/sumeet/projects/srp-client/node_modules/rsvp/dist/rsvp.js:525:12)
at invokeCallback (/Users/sumeet/projects/srp-client/node_modules/rsvp/dist/rsvp.js:538:13)
at /Users/sumeet/projects/srp-client/node_modules/rsvp/dist/rsvp.js:606:14
at flush (/Users/sumeet/projects/srp-client/node_modules/rsvp/dist/rsvp.js:2415:5)
at process._tickCallback (internal/process/next_tick.js:61:11)
- code: [undefined]
- codeFrame: Cannot read property '2' of null
- errorMessage: assets/test-support-ed34232ecba91175bdfd42b735eac4a9.js: Cannot read property '2' of null
in /var/folders/gy/vrp1632j5432m8f64r1n_c6m0000gn/T/broccoli-7006Xf9VxTec2khb/out-1291-fingerprint
at AssetRewrite
- errorType: Build Error
- location:
- column: [undefined]
- file: assets/test-support-ed34232ecba91175bdfd42b735eac4a9.js
- line: [undefined]
- treeDir: /var/folders/gy/vrp1632j5432m8f64r1n_c6m0000gn/T/broccoli-7006Xf9VxTec2khb/out-1291-fingerprint
- message: assets/test-support-ed34232ecba91175bdfd42b735eac4a9.js: Cannot read property '2' of null
in /var/folders/gy/vrp1632j5432m8f64r1n_c6m0000gn/T/broccoli-7006Xf9VxTec2khb/out-1291-fingerprint
at AssetRewrite
- name: BuildError
- nodeAnnotation: [undefined]
- nodeName: AssetRewrite
- originalErrorMessage: Cannot read property '2' of null
- stack: TypeError: Cannot read property '2' of null
at AssetRewrite.rewriteAssetPath (/Users/sumeet/projects/srp-client/node_modules/broccoli-asset-rewrite/index.js:127:91)
at AssetRewrite.processString (/Users/sumeet/projects/srp-client/node_modules/broccoli-asset-rewrite/index.js:167:24)
at AssetRewrite.processFile (/Users/sumeet/projects/srp-client/node_modules/broccoli-filter/index.js:165:31)
at asyncProcessFile (/Users/sumeet/projects/srp-client/node_modules/broccoli-filter/index.js:122:21)
at tryCatch (/Users/sumeet/projects/srp-client/node_modules/rsvp/dist/rsvp.js:525:12)
at invokeCallback (/Users/sumeet/projects/srp-client/node_modules/rsvp/dist/rsvp.js:538:13)
at /Users/sumeet/projects/srp-client/node_modules/rsvp/dist/rsvp.js:606:14
at flush (/Users/sumeet/projects/srp-client/node_modules/rsvp/dist/rsvp.js:2415:5)
at process._tickCallback (internal/process/next_tick.js:61:11)
```