Fluent NHibernate Cascade Issue - Trying To Insert NULL ID

Question

I have the following models & mappings (code snippets further below).

One Competition has to have multiple CompetitionAnswers associated with it (multiple choice

Answer 1

References(x => x.Competition)
    .Column("CompetitionId")
    .Not.Nullable(); //add this

and also make sure the child points to the parent in addition to the parent holding the child in it's collection. This is required when the parent is inverse.

a1.Competition = c; 

Was that column non null on database side but mapped as nullable on NH side?