empty_string = ""
not_empty_string = "a"

empty_string == ""
# => true
String.length(empty_string) == 0
# => true
byte_size(empty_string) == 0
# => true

not_empty_string == ""
# => false
String.length(not_empty_string) == 0
# => false
byte_size(not_empty_string) == 0
# => false