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

Quick tip: !obj.blank? == obj.present?

activesupport/lib/active_support/core_ext/object/blank.rb, line 17 # (Ruby 1.9) 

def present? 
 !blank?
end