Add workaround for lines==[nil] passed to auto_indent when exit IRB with CTRL+d

Author: tompng

lib/irb/ruby-lex.rb

@@ -94,6 +94,7 @@ def configure_io(io)
  if @io.respond_to?(:auto_indent) and @context.auto_indent_mode
  @io.auto_indent do |lines, line_index, byte_pointer, is_newline|
  next nil if !is_newline && lines[line_index]&.byteslice(0, byte_pointer)&.match?(/\A\s*\z/)
+ next nil if lines == [nil] # Workaround for exit IRB with CTRL+d
 
  code = lines[0..line_index].map { |l| "#{l}\n" }.join
  tokens = self.class.ripper_lex_without_warning(code, context: @context)