class Ougai::Formatters::Customizable

def default_err_format(trace_indent = 4)
  proc do |data|
    next nil unless data.key?(:err)
    err = data.delete(:err)
    err_str = "  #{err[:name]} (#{err[:message]}):"
    err_str += "\n" + (' ' * trace_indent) + err[:stack] if err.key?(:stack)
    err_str
  end
end