Make behavior clearer by returning false

Library/Homebrew/brew.rb

@@ -21,7 +21,7 @@ if ARGV == %w[--version] || ARGV == %w[-v]
 end
 
 def require?(path)
-  path ||= ""
+  return false if path.nil?
   require path
 rescue LoadError => e
   # we should raise on syntax errors but not if the file doesn't exist.