fix: support unknown file types by omitting content-type header

src/helpers/buildHeaders.js

@@ -20,9 +20,11 @@ module.exports.buildHeaders = function buildHeaders (
   let resolved = sourceFile
   const headers = {}
   const type = mime.getType(sourceFile.absolute)
+  if (type !== null) {
     headers['content-type'] = type.startsWith('text/')
       ? `${type}; charset=utf-8`
       : type
+  }
 
   const isImmutable = checkImmutable(sourceFile.absolute, immutablePatterns)
   headers['cache-control'] = isImmutable

test/fixtures/unknown-file-type/file.unknown

+Stuff
\ No newline at end of file

test/unknown-type.js

+const test = require('blue-tape')
+const { Master } = require('..')
+const { join } = require('path')
+const { h1 } = require('./helpers/receive')
+
+let master
+test('start server', async (t) => {
+  const cwd = join(__dirname, 'fixtures/unknown-file-type')
+  const options = {}
+  master = new Master({ cwd, options })
+  await master.listen()
+})
+
+test('Unknown file type', async (t) => {
+  const url = 'https://localhost:8443/file.unknown'
+  const response = await h1(url)
+  t.is(response.status, 200)
+  t.is(response.headers['content-type'], undefined)
+  t.is(await response.text(), 'Stuff')
+})
+
+test('stop server', async (t) => master.close())