Extensions to nil which allow for more helpful error messages for people who are new to Rails.

NilClass#id exists in Ruby 1.8 (though it is deprecated). Since id is a fundamental method of Active Record models NilClass#id is redefined as well to raise a RuntimeError and warn the user. She probably wanted a model database identifier and the 4 returned by the original method could result in obscure bugs.

The flag config.whiny_nils determines whether this feature is enabled. By default it is on in development and test modes, and it is off in production mode.

Methods
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Class Public methods
add_whiner(klass)

Source: show | on GitHub 

    # File activesupport/lib/active_support/whiny_nil.rb, line 15
15:   def self.add_whiner(klass)
16:     ActiveSupport::Deprecation.warn "NilClass.add_whiner is deprecated and this functionality is " \
17:       "removed from Rails versions as it affects Ruby 1.9 performance.", caller
18:   end
Instance Public methods
as_json(options = nil)

Source: show | on GitHub 

     # File activesupport/lib/active_support/json/encoding.rb, line 171
171:   def as_json(options = nil) self end
blank?()

nil is blank: 

  nil.blank? # => true

Source: show | on GitHub 

    # File activesupport/lib/active_support/core_ext/object/blank.rb, line 48
48:   def blank?
49:     true
50:   end
duplicable?()

nil is not duplicable: 

  nil.duplicable? # => false
  nil.dup         # => TypeError: can't dup NilClass

Source: show | on GitHub 

    # File activesupport/lib/active_support/core_ext/object/duplicable.rb, line 35
35:   def duplicable?
36:     false
37:   end
encode_json(encoder)

Source: show | on GitHub 

     # File activesupport/lib/active_support/json/encoding.rb, line 172
172:   def encode_json(encoder) 'null' end
id()

Raises a RuntimeError when you attempt to call id on nil.

Source: show | on GitHub 

    # File activesupport/lib/active_support/whiny_nil.rb, line 21
21:   def id
22:     raise RuntimeError, "Called id for nil, which would mistakenly be #{object_id} -- if you really wanted the id of nil, use object_id", caller
23:   end
to_param()

Source: show | on GitHub 

    # File activesupport/lib/active_support/core_ext/object/to_param.rb, line 9
 9:   def to_param
10:     self
11:   end
try(*args)

Calling try on nil always returns nil. It becomes specially helpful when navigating through associations that may return nil.

Examples

  nil.try(:name) # => nil

Without try 

  @person && !@person.children.blank? && @person.children.first.name

With try 

  @person.try(:children).try(:first).try(:name)

Source: show | on GitHub 

    # File activesupport/lib/active_support/core_ext/object/try.rb, line 54
54:   def try(*args)
55:     nil
56:   end