relationships property Null safety

All relationship values of this entity.

A relationship represents a value that is another ManagedObject or ManagedSet of ManagedObjects. Not all relationships correspond to a column or field in a database, only those with Relate metadata (see also ManagedRelationshipType.belongsTo). In this case, the underlying database column is a foreign key reference. The underlying database does not have storage for ManagedRelationshipType.hasMany or ManagedRelationshipType.hasOne properties, as those values are derived by the foreign key reference on the inverse relationship property. Keys are the case-sensitive name of the relationship.