In Ruby, you check with nil? if an object is nil:
article = nil
article.nil? # => true

empty? checks if an element - like a string or an array f.e. - is empty:

# Array
[].empty? #=> true
# String
"".empty? #=> true

Rails adds the method blank? to the Object class:

An object is blank if it‘s false, empty, or a whitespace string. For example, "", " ", nil, [], and {} are blank.

This simplifies

if !address.nil? && !address.empty?

to

if !address.blank?

.nil?

- It is Ruby method
- It can be used on any object and is true if the object is nil.
- "Only the object nil responds true to nil?" - RailsAPI nil.nil? = true
anthing_else.nil? = false
a = nil
a.nil? = true
“”.nil = false .empty? - It is Ruby method
- can be used on strings, arrays and hashes and returns true if:
  • String length == 0
  • Array length == 0
  • Hash length == 0

- Running .empty? on something that is nil will throw a NoMethodError "".empty = true
" ".empty? = false .blank? - It is Rails method
- operate on any object as well as work like .empty? on strings, arrays and hashes. nil.blank? = true
[].blank? = true
{}.blank? = true
"".blank? = true
5.blank? == false - It also evaluates true on strings which are non-empty but contain only whitespace: "  ".blank? == true"  ".empty? == false Quick tip: !obj.blank? == obj.present? activesupport/lib/active_support/core_ext/object/blank.rb, line 17 # (Ruby 1.9) def present?
 !blank?
end

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