add proper undefined checks

lib/src/http/response/FileResponseFactory.ts

@@ -38,7 +38,9 @@ export default class FileResponseFactory extends ResponseFactory {
         if ( content.headers && content.body && length ) {
             request.response.body = content.body
             request.response.headers.set('Content-Length', length)
-            request.response.headers.set('Content-Type', path.content_type)
+
+            if ( path.content_type )
+                request.response.headers.set('Content-Type', path.content_type)
         } else {
             this.logger.debug(`Tried to serve file that does not exist: ${path}`)
             request.response.status = HTTPStatus.NOT_FOUND

lib/src/support/UniversalPath.ts

@@ -102,6 +102,8 @@ export class UniversalPath {
     }
 
     get charset() {
-        return Mime.charset(this.mime_type)
+        if ( this.mime_type ) {
+            return Mime.charset(this.mime_type)
+        }
     }
 }