fix: Cannot read property 'filter' of null on Zeit

[adesege]

routes is null when using @nuxtjs/now-builder on Zeit. This fix sets an empty array when the variable null.

[codecov]

Codecov Report

Merging #95 into dev will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               dev       #95   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines          261       261           
  Branches        57        58    +1     
=========================================
  Hits           261       261           

Impacted Files	Coverage Δ
lib/module.js	100.00% <100.00%> (ø)

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[NicoPennec]

Thanks for your patch @adesege 🙏
But It seems not fix the root cause. Why the globalCache.staticRoutes is empty here?

sitemap-module/lib/generator.js

Line 42 in eaf2518

cache.staticRoutes = () => excludeRoutes(options.exclude, globalCache.staticRoutes)

I will investigate.

[adesege]

@NicoPennec globalCache.staticRoutes will hold static site routes and since the package can be used for both statically and universally generated sites, line 25 returns error if it can't find the sitemap-routes.json file in the dist folder.

I have updated line 26 to default to an empty array instead.