NoMethodError undefined method `[]=' for nil:NilClass - ruby-on-rails

Question

I created multiple classes with one test method to test wither the ruby objects get serialized correctly.
The error returned:
undefined method `[]=' for nil:NilClass
from /Users/horse/workspace/queryapi/app/models/query_model.rb:193:in `serialize'
I run the below test_query method through the rails console by initializing QueryModelTester and then invoking test_query() method on that object.
My code:
class QueryModelTester
def test_query
must = Must.new
range_criteria = RangeCriteria.new
range_criteria.gte = 20140712
range_criteria.lte = 1405134711
range = RangeBuilder.new
range.search_field = "created_time"
range.range_criteria = range_criteria
must.range = range
bool = Bool.new
bool.must = must
main_query = bool.serialize
puts main_query
end
end
Here are the model classes the above class is testing:
class RangeCriteria
#query_hash = Hash.new
attr_accessor :gte, :lte
def serialize
if(#gte.present?)
#query_hash[:gte] = #gte
end
if(#lte.present?)
#query_hash[:lte] = #lte
end
if(#gte.present? || #lte.present?)
return #query_hash
end
end
end
class RangeBuilder
#query_hash = Hash.new
attr_accessor :search_field, :range_criteria
def serialize
if(#search_field.present?)
#query_hash[#search_field] = #range_criteria.serialize
return #query_hash[:range] = #query_hash
end
end
end
class Bool
#query_hash = {}
attr_accessor :must
def serialize
if( #must.present? )
#query_hash[:must] = #must.serialize
return #query_hash[:bool] = #query_hash
end
end
end

Answer 1

The problem is when you initialize your #query_hash. In all your classes they are initialized in wrong scope. To fix it, you should move #query_hash = Hash.new to initialize method, like:
class RangeCriteria
def initialize
#query_hash = Hash.new
end
# ...
end
class RangeBuilder
def initialize
#query_hash = Hash.new
end
# ...
end
class Bool
def initialize
#query_hash = Hash.new
end
# ...
end
Hope that helps.
Good luck!