TypeError: Invalid value "null" for header "content-type" (lib/plugins/static.js)

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Bug Report

Restify Version

8.2.0

Node.js Version

10.15.3

Expected behaviour

I can serve static files over HTTP/2 without errors

Actual behaviour

internal/http2/compat.js:66
throw err;
^

TypeError [ERR_HTTP2_INVALID_HEADER_VALUE]: Invalid value "null" for header "content-type"
at Http2ServerResponse.[setHeader] (internal/http2/compat.js:543:5)
at Http2ServerResponse.setHeader (internal/http2/compat.js:538:21)
at Http2ServerResponse.header (/app/node_modules/restify/lib/response.js:226:14)
at Http2ServerResponse.set (/app/node_modules/restify/lib/response.js:548:18)
at ReadStream.onceOpen (/app/node_modules/restify/lib/plugins/static.js:118:17)
at Object.onceWrapper (events.js:277:13)
at ReadStream.emit (events.js:189:13)
at ReadStream.EventEmitter.emit (domain.js:441:20)
at lazyFs.open (internal/fs/streams.js:120:10)
at FSReqWrap.args [as oncomplete] (fs.js:140:20)

Repro case

import Restify from 'restify';
import { readFileSync } from 'fs';

const cert = readFileSync(...);
const key = readFileSync(...);
const server = Restify.createServer({ http2: { cert, key, allowHTTP1: false } });
server.get('/*', Restify.plugins.serveStatic({
    directory: path.join(__dirname, '../static'),
    default: 'index.html'
  }));
server.listen(443);

Then you make a HTTP request for a CUR file (for example):

GET https://localhost/images/openhand.cur

Cause

/lib/plugins/static.js:118:17

mime.getType() returns null, which is not accepted by Http2ServerResponse.setHeader

Are you willing and able to fix this?

Yes, I have a fix and can make a Pull Request:

https://github.com/drash-course/node-restify/tree/content-type-patch

Review lib/plugins/static.js at line 118, where mime.getType() supplies the content-type for a served static file. Reproduce the HTTP/2 request for a CUR file, then verify that serving files with an unknown MIME type no longer passes null to the response header.