Resolving Jekyll Serve Error: Liquid Exception: undefined method gsub’ for nil:NilClass`

Problem

  Liquid Exception: undefined method `gsub' for nil:NilClass in _includes/post_pagination.html, included in _layouts/single.html
jekyll 3.0.3 | Error:  undefined method `gsub' for nil:NilClass

This error was triggered by the following jekyll serve command:

$ make run
bundle exec jekyll serve --config _config.localhost.yml --drafts
Configuration file: _config.localhost.yml
            Source: /Users/too1/Development/blog.justintoo.com
       Destination: /Users/too1/Development/blog.justintoo.com/_site
 Incremental build: disabled. Enable with --incremental
      Generating...
  Liquid Exception: undefined method `gsub' for nil:NilClass in _includes/post_pagination.html, included in _layouts/single.html
jekyll 3.0.3 | Error:  undefined method `gsub' for nil:NilClass
make: *** [run] Error 1

I ran into this issue while trying to start the Jekyll server on my local development machine to view this Github Pages blog.

Solution

It turns out the problem was simply that my newly added draft post was missing the meta information at the top of the Markdown file:

# draft-post.md
---
title: "My draft post title"
---

So I added this section and voila, problem solved!

$ bundle exec jekyll serve --config _config.localhost.yml
Configuration file: _config.localhost.yml
            Source: /Users/too1/Development/blog.justintoo.com
       Destination: /Users/too1/Development/blog.justintoo.com/_site
 Incremental build: disabled. Enable with --incremental
      Generating...
                    done in 2.326 seconds.
 Auto-regeneration: enabled for '/Users/too1/Development/blog.justintoo.com'
Configuration file: _config.localhost.yml
    Server address: http://127.0.0.1:4000/
  Server running... press ctrl-c to stop.

Environment

Item	Description
Git	git version 2.6.4 (Apple Git-63)
Jekyll	jekyll 3.0.3
Operating System	OS X El Capitan version 10.11.6
Ruby	ruby 2.3.3p222 (2016-11-21 revision 56859) [x86_64-darwin15]