How to modify treeBuilder.Dot to generate LEFT JOIN instead of INNER JOIN in custom function generator for NHibernate?

Question

Im trying to extend LINQ to NHibernate provider for my custom function. The problem that I found is that, whenever I try to access a FK from my entity, it generates a "INNER JOIN" statement, but I want to have a LEFT JOIN, so I have all the "DistributorAnswers" where the "Distributor" FK is null.
Here's the BuildHql:

public override HqlTreeNode BuildHql(MethodInfo method, Expression targetObject,
            ReadOnlyCollection<Expression> arguments,
            HqlTreeBuilder treeBuilder, IHqlExpressionVisitor visitor)
        {
            var targetNode = visitor.Visit(targetObject).AsExpression();
            return treeBuilder.Dot(targetNode, treeBuilder.Ident(nameof(DistributorAnswer.Distributor)));
        }

The generated SQL query currently uses an INNER JOIN, and I need to modify it to use a LEFT JOIN instead.
Here's the query output that I found with SQL Server Profiler

EXEC sp_executesql N'select TOP (@p0)
 ...
from [DistributorAnswer] distributo0_ 
inner join [Distributor] distributo1_ on distributo0_.Distributor_id=distributo1_.Id

And here's the LINQ that i'm trying to run with my custom function:

Session.Query<DistributorAnswer>()
                .Select(x => x.MyCustomMethod())
                .Take(10)
                .ToList();

The problem I am facing is that I don't know how to modify the treeBuilder.Dot method to generate the desired LEFT JOIN. I have examined the available methods and properties in the HqlTreeBuilder class, but I couldn't find a direct way to specify the join type.

I tried to use treeBuilder.LeftJoin but I cannot find any documentation about this and I really don't understand how it works.

Thank you in advance for your help!