500 error on read public document - NamedNode IRI "null" must be absolute.

A strange obug. When the document is read by a webapp it gets a 500 error, but a simple curl gives 200.

$ curl -I https://solidos.solidcommunity.net/public/2021/10_example_data/example.ttl
HTTP/1.1 200 OK
X-Powered-By: solid-server/5.6.16
Vary: Accept, Authorization, Origin
Access-Control-Allow-Credentials: true
Access-Control-Expose-Headers: Authorization, User, Location, Link, Vary, Last-Modified, ETag, Accept-Patch, Accept-Post, Updates-Via, Allow, WAC-Allow, Content-Length, WWW-Authenticate, MS-Author-Via, X-Powered-By
Allow: OPTIONS, HEAD, GET, PATCH, POST, PUT, DELETE
Link: <example.ttl.acl>; rel="acl", <example.ttl.meta>; rel="describedBy", <http://www.w3.org/ns/ldp#Resource>; rel="type"
WAC-Allow: user="read write append",public="read write append"
MS-Author-Via: SPARQL
Updates-Via: wss://solidos.solidcommunity.net
Content-Type: text/turtle; charset=utf-8
Content-Length: 2
ETag: W/"2-nOO9QiTIwXgNtWtBJezz8kv3SLc"
Date: Tue, 16 Nov 2021 23:45:39 GMT
Connection: keep-alive
Keep-Alive: timeout=5

but the same URI when fetched by mashlib gives 500

HTTP/1.1 500 Internal Server Error
X-Powered-By: solid-server/5.6.16
Access-Control-Allow-Origin: null
Vary: Accept, Authorization, Origin
Access-Control-Allow-Credentials: true
Access-Control-Expose-Headers: Authorization, User, Location, Link, Vary, Last-Modified, ETag, Accept-Patch, Accept-Post, Updates-Via, Allow, WAC-Allow, Content-Length, WWW-Authenticate, MS-Author-Via, X-Powered-By
Allow: OPTIONS, HEAD, GET, PATCH, POST, PUT, DELETE
Link: <example.ttl.acl>; rel="acl", <example.ttl.meta>; rel="describedBy", <http://www.w3.org/ns/ldp#Resource>; rel="type"
Content-Type: text/plain; charset=utf-8
Content-Length: 39
ETag: W/"27-AVbkXABETaBBBb89giO49PTSQHQ"
Date: Tue, 16 Nov 2021 23:52:01 GMT
Connection: keep-alive
Keep-Alive: timeout=5

where it looks ss though the server log may look something like

0|solid  | 2021-11-16T23:32:33.227Z solid:server Error page because of: Error: NamedNode IRI "null" must be absolute.
0|solid  |     at new NamedNode (/Users/timbl/src/github.com/solid/node-solid-server/node_modules/rdflib/lib/named-node.js:64:13)
0|solid  |     at Object.namedNode (/Users/timbl/src/github.com/solid/node-solid-server/node_modules/rdflib/lib/factories/canonical-data-factory.js:150:12)
0|solid  |     at new ACLChecker (/Users/timbl/src/github.com/solid/node-solid-server/lib/acl-checker.js:31:74)
0|solid  |     at Function.createFromLDPAndRequest (/Users/timbl/src/github.com/solid/node-solid-server/lib/acl-checker.js:189:12)
0|solid  |     at allowHandler (/Users/timbl/src/github.com/solid/node-solid-server/lib/handlers/allow.js:47:21)
0|solid  | /Users/timbl/src/github.com/solid/node-solid-server/lib/handlers/allow.js:78
0|solid  |     const error = req.authError || await req.acl.getError(userId, mode)
0|solid  |                                                  ^
0|solid  | TypeError: Cannot read properties of undefined (reading 'getError')
0|solid  |     at allowHandler (/Users/timbl/src/github.com/solid/node-solid-server/lib/handlers/allow.js:78:50)

and the httop response body is

NamedNode IRI "null" must be absolute.

Tái hiện sự khác biệt giữa yêu cầu curl và yêu cầu của ứng dụng web mashlib, sau đó kiểm tra lib/acl-checker.js quanh các dòng 31 và 189 cũng như lib/handlers/allow.js quanh các dòng 47 và 78. Truy tìm lý do đường dẫn webapp tạo ra một NamedNode null và xác minh rằng việc đọc tài liệu công khai không còn trả về lỗi 500.