Accessing instance variables from outside the class

I'm having issues understanding this encapsulation. I have instance variables defined with attr_accessor. I'm trying to access them outside class. But they are always nil and returns undefined method.

NoMethodError: undefined method `has_key?' for nil:NilClass

Please help me understand.

class TrieNode
    attr_reader :value, :next, :children
    
    def initalize
        @value = nil
        @children = Hash.new
        @next = nil
    end
end

class Trie
    attr_accessor :root
    
    def initialize
        @root = TrieNode.new
    end
    
    def build_trie(strs)
        cur = @root
        
        strs.each do |str|
            str.chars.each do |char|
                if cur.children.has_key? char
                    cur = cur.children[char]
                    next
                else
                    new_node = TrieNode.new
                    cur.children[char] = new_node
                    cur = new_node
                end
            end
          cur = @root
        end
    end
end