**Apache Airflow version**: 2.1.0

**Browsers**: Chrome and Firefox

**What happened**:

Before upgrading to 2.1.0

![before](https://user-images.githubusercontent.com/14293802/120359517-c1ca1100-c2d5-11eb-95ba-58ccc0a3ac37.png)

After upgrading to 2.1.0

![after](https://user-images.githubusercontent.com/14293802/120359528-c4c50180-c2d5-11eb-8e04-f34846ea2736.png)

**What you expected to happen**:

Show/Edit/Delete under Security -> Users are available

<!-- What do you think went wrong? -->

**How to reproduce it**:

Go to Security -> Users (as an admin of course) 
airflow/www/views.py
for source_id in task_group.upstream_task_ids:
            edges_to_add.add((source_id, task_group.upstream_join_id))
            for child in task_group.get_roots():
                edges_to_add.add((task_group.upstream_join_id, child.task_id))
                edges_to_skip.add((source_id, child.task_id))
        for child in task_group.children.values():
            collect_edges(child)
    collect_edges(dag.task_group)
    
    edges = set()
    def get_downstream(task):
        for child in task.downstream_list:
            edge = (task.task_id, child.task_id)
            if edge not in edges:
                edges.add(edge)
                get_downstream(child)
    for root in dag.roots:
        get_downstream(root)
    result = []
    
    
    for source_id, target_id in sorted(edges.union(edges_to_add) - edges_to_skip):
        record = {"source_id": source_id, "target_id": target_id}
        label = dag.get_edge_info(source_id, target_id).get("label")
        if label:
            record["label"] = label
        result.append(record)
    return result
def circles(error):