Check wether prompt_i is nil

1 files changed, 2 insertions, 1 deletions

diff --git a/lib/irb.rb b/lib/irb.rb
index 2b00de9f62..f9c27782b9 100644
--- a/lib/irb.rb
+++ b/lib/irb.rb
@@ -463,7 +463,8 @@ module IRB
         end
         if @context.auto_indent_mode and !@context.io.respond_to?(:auto_indent)
           unless ltype
-            ind = prompt(@context.prompt_i, ltype, indent, line_no)[/.*\z/].size +
+            prompt_i = @context.prompt_i.nil? ? "" : @context.prompt_i
+            ind = prompt(prompt_i, ltype, indent, line_no)[/.*\z/].size +
               indent * 2 - p.size
             ind += 2 if continue
             @context.io.prompt = p + " " * ind if ind > 0