Linking cards from empty board is possible and makes current board not load anymore

[ymeramees]

Issue

Server Setup Information: Ubuntu 16.04.5 LTS

• Did you test in newest Wekan?: yes
• Wekan version: 1.43.0
• Operating System: Ubuntu 16.04.5 LTS
• Deployment Method(snap/docker/sandstorm/mongodb bundle/source): source
• Http frontend if any (Caddy, Nginx, Apache, see config examples from Wekan GitHub wiki first): -
• Node Version: v8.11.3
• MongoDB Version: 2.6.10

Problem description: When linking a card from a board which doesn't have any cards, an empty card will be created in MongoDB. This results that the board to which this was linked will not load anymore. After deleting the created linked-card from db with help of Mongo console, board could be loaded again.

There should probably be some kind of check that all fields are filled. Currently it is possible to continue with empty cards field:

• Explain steps how to reproduce

1. Create two empty boards
2. Link card from first board to the second one. There will be no cards to choose, but still click on "link".
3. Try to reload second board.

• Attach log files in .zip file)
  Card created in db:
  {
  "_id" : "wdijvfEdwzNMFHoG9",
  "listId" : "5EBs85kXpwK5p4j6C",
  "swimlaneId" : "3i2PdKPezcTDfRAGG",
  "boardId" : "5oC6XfE5FY9QDt2Xu",
  "sort" : 3,
  "type" : "cardType-linkedCard",
  "title" : "",
  "archived" : false,
  "parentId" : "",
  "coverId" : "",
  "createdAt" : ISODate("2018-09-09T06:32:06.553Z"),
  "customFields" : [ ],
  "dateLastActivity" : ISODate("2018-09-09T06:32:06.554Z"),
  "description" : "",
  "requestedBy" : "",
  "assignedBy" : "",
  "labelIds" : [ ],
  "members" : [ ],
  "spentTime" : 0,
  "isOvertime" : false,
  "userId" : "RR6rMEeaGmh33iLN5",
  "subtaskSort" : -1,
  "linkedId" : ""
  }