diff --git a/Library/Homebrew/brew.rb b/Library/Homebrew/brew.rb
index 9b2ff75f0c..03eeb8a187 100644
--- a/Library/Homebrew/brew.rb
+++ b/Library/Homebrew/brew.rb
@@ -21,6 +21,7 @@ if ARGV == %w[--version] || ARGV == %w[-v]
 end
 
 def require?(path)
+  path ||= ""
   require path
 rescue LoadError => e
   # we should raise on syntax errors but not if the file doesn't exist.
diff --git a/Library/Homebrew/cask/lib/hbc/cli.rb b/Library/Homebrew/cask/lib/hbc/cli.rb
index c8fe391717..37784f4c3c 100644
--- a/Library/Homebrew/cask/lib/hbc/cli.rb
+++ b/Library/Homebrew/cask/lib/hbc/cli.rb
@@ -113,7 +113,7 @@ module Hbc
       if command.respond_to?(:run)
         # usual case: built-in command verb
         command.run(*rest)
-      elsif require?(which("brewcask-#{command}.rb").to_s)
+      elsif require?(which("brewcask-#{command}.rb"))
         # external command as Ruby library on PATH, Homebrew-style
       elsif command.to_s.include?("/") && require?(command.to_s)
         # external command as Ruby library with literal path, useful