ruby on rails - How to solve the undefined method '[]' for nilClass error? -

i keep getting following error every time run code

undefined method '[]' nilclass: nomethoderror 

there 2 classes, lineanalyzer , solution class , problem seems in lineanalyzer calculate_word_frequency method couldn't find error.

the code shown below:

class lineanalyzer   attr_accessor :highest_wf_count, :highest_wf_words, :linescount, :content , :line_number    @highest_wf_count = hash.new(0)   @highest_wf_words = array.new(0)   @content    @line_number    def initialize(line, line_num)     @content = line     @line_number = line_num     calculate_word_frequency()   end    def calculate_word_frequency()     @content.split.each |word|       @highest_wf_count[word.downcase] += 1     end     max = 0     @highest_wf_count.each_pair |key, value|        if value > max          max = value       end     end     word_frequency.each_pair |key, value|        if value == max          @highest_wf_words << key       end     end    end end  class solution   attr_accessor :highest_count_across_lines, :highest_count_words_across_lines, :line_analyzers    @highest_count_across_lines = hash.new()   @highest_count_words_across_lines = hash.new()   @line_analyzers = array.new()    def analyze_file     line_count = 0     x = file.foreach('c:\x\test.txt')     x.each |line|       line_count += 1       @line_analyzers << lineanalyzer.new(line, line_count)     end   end end  solution = solution.new # expect errors until implement these methods solution.analyze_file 

any appreciated.

it looks issue when trying increment word_count first time word seen, hash using doesn't have key, can't increment it. first time key seen, should set 1, , occurrences should increment it:

class lineanalyzer     attr_accessor :highest_wf_count, :highest_wf_words, :linescount, :content , :line_number      def initialize(line,line_num)         @highest_wf_count = hash.new(0)         @highest_wf_words = array.new(0)         @content = line         @line_number = line_num         calculate_word_frequency()     end     def calculate_word_frequency()        @content.split.each |word|            highest_wf_count.key?(word.downcase) ? @highest_wf_count[word.downcase]+=1 : @highest_wf_count[word.downcase]=1        end        max =0         @highest_wf_count.each_pair |key, value|             if value > max                max = value            end         end        highest_wf_count.each_pair |key, value|            if value == max               @highest_wf_words << key           end        end      end end  class solution     attr_accessor :highest_count_across_lines, :highest_count_words_across_lines, :line_analyzers     @highest_count_across_lines = hash.new()     @highest_count_words_across_lines = hash.new()      def analyze_file       line_count = 0       x = file.foreach('c:\x\test.txt')       x.each{ |line|         line_count +=1         line_analyzer << lineanalyzer.new(line,line_count)       }       puts "line_analyzer: #{line_analyzer.inspect}"    end      def line_analyzer         @line_analyzers ||= array.new     end end