I have this obviously incorrect code:

mixin TestMix
{
 abstract |->Bool| taut := |->Bool| {return true}
}

And compiler goes haywire:

ERR: Internal compiler error
sys::NullErr: java.lang.NullPointerException
  compiler::ResolveExpr.localsInScope (ResolveExpr.fan:857)
  compiler::ResolveExpr.resolveClosure (ResolveExpr.fan:713)
  compiler::ResolveExpr.resolveExpr (ResolveExpr.fan:174)
  compiler::ResolveExpr.visitExpr (ResolveExpr.fan:123)
  compiler::Expr.walk (Expr.fan:253)
  compiler::FieldDef.walk (FieldDef.fan:70)
  compiler::TypeDef.walk (TypeDef.fan:311)
  fan.sys.List.each (List.java:527)
  compiler::TypeDef.walk (TypeDef.fan:311)
  compiler::Visitor.walk (Visitor.fan:31)
  fan.sys.List.each (List.java:527)
  compiler::Visitor$.walk (Visitor.fan:31)
  compiler::CompilerStep.walk (CompilerStep.fan:14)
  compiler::ResolveExpr.run (ResolveExpr.fan:37)
  compiler::Compiler.frontend (Compiler.fan:90)
  compiler::Compiler.compile (Compiler.fan:64)
  build::BuildPod.compileFan (BuildPod.fan:214)
  build::BuildPod.compile (BuildPod.fan:162)
  java.lang.reflect.Method.invoke (Unknown)
  fan.sys.Method.invoke (Method.java:552)
  20 More...

Promoted to ticket #1564 and assigned to brian

Ticket resolved in 1.0.61