Why is `a = a` `nil` in Ruby?

Why is `a = a` `nil` in Ruby?

ruby variable-assignment local-variables

ruby

Double Pipe Symbols in Ruby Variable Assignment? [duplicate]

ruby boolean variable-assignment

ruby

How to assign hash['a']['b']= 'c' if hash['a'] doesn't exist?

ruby hash variable-assignment autovivification hash-of-hashes

ruby

Ruby double pipe assignment with block/proc/lambda?

ruby syntax operators variable-assignment block

ruby

Block scope in ruby

ruby scope variable-assignment block

ruby

How does Ruby handle assignment semantically?

ruby variable-assignment assignment-operator

ruby

Assign variable only if not nil

ruby null variable-assignment

ruby

Scope of a local variable in a block

ruby block variable-assignment

ruby