How to write a lambda parameter?

[liyihuanx]

i want to write (e: Exception) -> Unit)? = null as a parameter. how can i do? please help!!!!

[Egorand]

Start with a ParameterSpec.builder() and create a LambdaTypeName to represent the type. To provide the default null argument, use ParameterSpec.Builder.defaultValue(). There should be a few similar examples in the unit tests.