isNotNull method
Adds a 'not null check' expression to a query.
A query will only return objects where the selected property is not null.
This method can be applied to any property type.
Example:
var q = new Query<Employee>()
..where((e) => e.manager).isNotNull();
Implementation
QueryExpressionJunction<T, InstanceType> isNotNull() {
expression = const NullCheckExpression(shouldBeNull: false);
return _createJunction();
}