Infinite loading when aggregate $lookup is not used correctly

[daniil-konovalenko]

I ran the following query:

db.Projects.aggregate([{
  $lookup: {
    from: 'ProjectTypes',
    localField: 'project_type_id',
    foreign_field: '_id',
    as: 'types'
  }
}])

Normally this query would result in an error:

Error: command failed: {
	"ok" : 0,
	"errmsg" : "unknown argument to $lookup: foreign_field",
	"code" : 9,
	"codeName" : "FailedToParse"
} : aggregate failed :

However, mongotron ingnored the error and just showed the usual loading spinner.