Question

I seem to have a Mono problem that I cannot duplicate in my Windows test environment where I get a YSOD that looks like this:

Server Error in '/' Application

Object reference not set to an instance of an object

Description: HTTP 500. Error processing request.

Stack Trace:

System.NullReferenceException: Object reference not set to an instance of an object
  at FluentNHibernate.Visitors.DefaultMappingModelVisitor.Visit (FluentNHibernate.MappingModel.ColumnMapping columnMapping) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.MappingModel.KeyMapping.AcceptVisitor (IMappingModelVisitor visitor) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.Visitors.DefaultMappingModelVisitor.Visit (FluentNHibernate.MappingModel.KeyMapping keyMapping) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.MappingModel.ClassBased.SubclassMapping.AcceptVisitor (IMappingModelVisitor visitor) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.Visitors.DefaultMappingModelVisitor.Visit (FluentNHibernate.MappingModel.ClassBased.SubclassMapping subclassMapping) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.MappingModel.ClassBased.ClassMappingBase.AcceptVisitor (IMappingModelVisitor visitor) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.MappingModel.ClassBased.ClassMapping.AcceptVisitor (IMappingModelVisitor visitor) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.Visitors.DefaultMappingModelVisitor.Visit (FluentNHibernate.MappingModel.ClassBased.ClassMapping classMapping) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.MappingModel.HibernateMapping.AcceptVisitor (IMappingModelVisitor visitor) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.Visitors.DefaultMappingModelVisitor.<Visit>b__0 (FluentNHibernate.MappingModel.HibernateMapping x) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.Utils.CollectionExtensions.Each[HibernateMapping] (IEnumerable`1 enumerable, System.Action`1 each) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.Visitors.DefaultMappingModelVisitor.Visit (IEnumerable`1 mappings) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.PersistenceModel.ApplyVisitors (IEnumerable`1 mappings) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.PersistenceModel.BuildMappings () [0x00000] in <filename unknown>:0 
  at FluentNHibernate.PersistenceModel.EnsureMappingsBuilt () [0x00000] in <filename unknown>:0 
  at FluentNHibernate.PersistenceModel.Configure (NHibernate.Cfg.Configuration cfg) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.Cfg.MappingConfiguration.Apply (NHibernate.Cfg.Configuration cfg) [0x00000] in <filename unknown>:0 
  at FluentNHibernate.Cfg.FluentConfiguration.BuildConfiguration () [0x00000] in <filename unknown>:0 
Version information: Mono Runtime Version: 2.10.8.1 (Debian 2.10.8.1-1ubuntu2.2); ASP.NET Version: 4.0.30319.1

I’m scratching my head how to go about troubleshooting this. The standard debugging tools are conspicuously absent. Is there some mechanism to collect line numbers and context information to research this issue?

Answer 1

OK, I figured this out but the answer is too long for here. I blogged about it (and yes I admit it’s a kludge) here.