///assembly one... public class AnExternalClass: public static def Do[of T](p as T): pass ///assembly two... class Class2: pass c = Class2() AnExternalClass.Do[of Class2](c) Results in the following error included below. The included patch fixes this. The method EmitAsssembly.CheckConditionalAttributes was assuming that GenericConstructedMethod.GenericDefinition would be of type InternalMethod. But it can also be of type ExternalMethod. test01.boo(34,30): Internal compiler error on node 'AnExternalClass.Do[of Class2](c)': System.NullReferenceException: Object reference not set to an instance of an object. at Boo.Lang.Compiler.Steps.EmitAssembly.CheckConditionalAttributes(IMethod method, MethodInfo mi) in C:\boo_svn_ms\src\Boo.Lang.Compiler\Steps\EmitAssembly.cs:line 2107 at Boo.Lang.Compiler.Steps.EmitAssembly.InvokeRegularMethod(IMethod method, MethodInfo mi, MethodInvocationExpression node) in C:\boo_svn_ms\src\Boo.Lang.Compiler\Steps\EmitAssembly.cs:line 2064 at Boo.Lang.Compiler.Steps.EmitAssembly.InvokeMethod(IMethod method, MethodInvocationExpression node) in C:\boo_svn_ms\src\Boo.Lang.Compiler\Steps\EmitAssembly.cs:line 2021 at Boo.Lang.Compiler.Steps.EmitAssembly.OnMethodInvocationExpression(MethodInvocationExpression node) in C:\boo_svn_ms\src\Boo.Lang.Compiler\Steps\EmitAssembly.cs:line 2349 at Boo.Lang.Compiler.Ast.MethodInvocationExpression.Accept(IAstVisitor visitor) in C:\boo_svn_ms\src\Boo.Lang.Compiler\Ast\Impl\MethodInvocationExpressionImpl.cs:line 67 at Boo.Lang.Compiler.Ast.DepthFirstVisitor.Visit(Node node) in C:\boo_svn_ms\src\Boo.Lang.Compiler\Ast\DepthFirstVisitor.cs:line 42