Return false in Dag.equals if other.dag is null
Test if Dag.equals handles nulls correctly
Also check this.dag for null value
Rewrite hashCode and equals
They now both use the id
Remove Dag-specific code that was moved to DagApplicationTest
Add hashCode()
Remove null check and check equality instead
null is checked later, the equality check should increase performance
Add checks for null values
Test if Dag with Dag.dag == null equals itself
Use super's equal instead of accidentally recursing
Get attendances form DB and add them to the bound Kind before saving
Fixes #1