C# / .NET fluent query

Elastic Stack Elasticsearch
1

Let's assume the following:

var Match = EC.Search(_ => _
.Query(Q => Q.Term(P => P.Category, (int)Category)
.Query(Q => Q.Term(P => P.Type, (int)Type));

Does this mean Query1 AND Query2, or Query 1 OR Query2?

Now if I do create a conditional query:

var Match = EC.Search(_ => _
.Query(Q =>
{
if (a > b) return Q.Term(P => P.Mine, true);
else return null;
}
Query(Q => Q.Term(P => P.Category, (int)Category)
.Query(Q => Q.Term(P => P.Type, (int)Type));

If I do this, does returning null allow to completely ignore this query? I just want to add this piece IF the condition a > b is true

And, last, if I use some operators:

var Match = EC.Search(_ => _
.Query(Q =>
Q.Term(P => P.Category, (int)Category)
&& Q.Term(P => P.Type, (int)Type));

How can I use a lambda expression in the query?

var Match = EC.Search(_ => _
.Query(Q =>
{ .... }
&& Q.Term(P => P.Category, (int)Category)
&& Q.Term(P => P.Type, (int)Type));

will not compile....