class Rubocop::Cop::Style::DefWithParentheses

class/singleton methods are checked.
that does not take any arguments. Both instance and
This cop checks for parentheses in the definition of a method,

def on_def(node) 

def on_def(node)
  start_line = node.loc.keyword.line
  end_line = node.loc.end.line
  return if start_line == end_line
  _, args = *node
  if args.children == [] && args.loc.begin
    add_offence(:convention, args.loc.begin, MSG)
  end
  super
end

def on_defs(node) 

def on_defs(node)
  start_line = node.loc.keyword.line
  end_line = node.loc.end.line
  return if start_line == end_line
  _, _, args = *node
  if args.children == [] && args.loc.begin
    add_offence(:convention, args.loc.begin, MSG)
  end
  super
end