Can't query EmbeddedDocumentListField with parameters

EmbeddedDocumentListField can't be queried with parameters.

Running the example at https://github.com/graphql-python/graphene-mongo/tree/master/examples/flask_mongoengine
and replacing the query with
```
{
allEmployees {
edges {
node {
id,
name,
department {
id,
name
},
roles {
edges {
node {
id,
name
}
}
},
leader {
id,
name
}
tasks(last:1) { # note the parameter here
edges {
node {
name,
deadline
}
}
}
}
}
}
}
```
we get the errors
```
"errors": [
{
"message": "'Task' object has no attribute 'pk'",
"locations": [
{
"line": 23,
"column": 9
}
],
"path": [
"allEmployees",
"edges",
1,
"node",
"tasks"
]
},
{
"message": "'Task' object has no attribute 'pk'",
"locations": [
{
"line": 23,
"column": 9
}
],
"path": [
"allEmployees",
"edges",
2,
"node",
"tasks"
]
}
]
```
How to solve this ?

Beginnen Sie damit, die Abfrage in examples/flask_mongoengine zu reproduzieren, insbesondere tasks(last:1) für das EmbeddedDocumentListField. Verfolgen Sie den Pfad, der die Fehler "Task" object has no attribute "pk" erzeugt, und betrachten Sie das Issue als abgeschlossen, wenn parametrisierte tasks gültige edges ohne diese Fehler zurückgeben.

Vom Indexierungsmodell aus dem Issue-Text verfasst.