Be more clear about what we do when the description is nil

Author: benoittgt

lib/rspec/core/formatters/exception_presenter.rb

@@ -245,7 +245,8 @@ def formatted_message_and_backtrace(colorizer)
         end
 
         def encoded_description(description)
-          encoded_string(description) if description
+          return if description.nil?
+          encoded_string(description)
         end
 
         def exception_backtrace