diff --git a/modules/openapi-generator/src/main/resources/crystal/api.mustache b/modules/openapi-generator/src/main/resources/crystal/api.mustache
index 550f017c4c6..8b8daabb5f3 100644
--- a/modules/openapi-generator/src/main/resources/crystal/api.mustache
+++ b/modules/openapi-generator/src/main/resources/crystal/api.mustache
@@ -55,7 +55,7 @@ module {{moduleName}}
       {{^isContainer}}
       # verify enum value
       allowable_values = [{{#allowableValues}}{{#enumVars}}{{{value}}}{{^-last}}, {{/-last}}{{/enumVars}}{{/allowableValues}}]
-      if @api_client.config.client_side_validation && !allowable_values.include?({{{paramName}}})
+      if @api_client.config.client_side_validation && !allowable_values.includes?({{{paramName}}})
         raise ArgumentError.new("invalid value for \"{{{paramName}}}\", must be one of #{allowable_values}")
       end
       {{/isContainer}}
@@ -66,13 +66,13 @@ module {{moduleName}}
       {{#isEnum}}
       {{#collectionFormat}}
       allowable_values = [{{#allowableValues}}{{#enumVars}}{{{value}}}{{^-last}}, {{/-last}}{{/enumVars}}{{/allowableValues}}]
-      if @api_client.config.client_side_validation && {{{paramName}}} && {{{paramName}}}.all? { |item| allowable_values.include?(item) }
+      if @api_client.config.client_side_validation && {{{paramName}}} && {{{paramName}}}.all? { |item| allowable_values.includes?(item) }
         raise ArgumentError.new("invalid value for \"{{{paramName}}}\", must include one of #{allowable_values}")
       end
       {{/collectionFormat}}
       {{^collectionFormat}}
       allowable_values = [{{#allowableValues}}{{#enumVars}}{{{value}}}{{^-last}}, {{/-last}}{{/enumVars}}{{/allowableValues}}]
-      if @api_client.config.client_side_validation && {{{paramName}}} && !allowable_values.include?({{{paramName}}}])
+      if @api_client.config.client_side_validation && {{{paramName}}} && !allowable_values.includes?({{{paramName}}})
         raise ArgumentError.new("invalid value for \"{{{paramName}}}\", must be one of #{allowable_values}")
       end
       {{/collectionFormat}}
diff --git a/modules/openapi-generator/src/main/resources/crystal/api_client.mustache b/modules/openapi-generator/src/main/resources/crystal/api_client.mustache
index 5352175b00e..6831e51bae0 100644
--- a/modules/openapi-generator/src/main/resources/crystal/api_client.mustache
+++ b/modules/openapi-generator/src/main/resources/crystal/api_client.mustache
@@ -342,7 +342,7 @@ module {{moduleName}}
         :verbose => @config.debugging
       }
 
-      if [:post, :patch, :put, :delete].include?(http_method)
+      if [:post, :patch, :put, :delete].includes?(http_method)
         req_body = build_request_body(header_params, form_params, opts[:body])
         req_opts.update body: req_body
         if @config.debugging
diff --git a/modules/openapi-generator/src/main/resources/crystal/api_client_faraday_partial.mustache b/modules/openapi-generator/src/main/resources/crystal/api_client_faraday_partial.mustache
index dfef217e037..d1782b5e348 100644
--- a/modules/openapi-generator/src/main/resources/crystal/api_client_faraday_partial.mustache
+++ b/modules/openapi-generator/src/main/resources/crystal/api_client_faraday_partial.mustache
@@ -81,7 +81,7 @@
         :verbose => @config.debugging
       }
 
-      if [:post, :patch, :put, :delete].include?(http_method)
+      if [:post, :patch, :put, :delete].includes?(http_method)
         req_body = build_request_body(header_params, form_params, opts[:body])
         req_opts.update body: req_body
         if @config.debugging
diff --git a/modules/openapi-generator/src/main/resources/crystal/api_client_typhoeus_partial.mustache b/modules/openapi-generator/src/main/resources/crystal/api_client_typhoeus_partial.mustache
index d8e95e77461..e076e92c9fd 100644
--- a/modules/openapi-generator/src/main/resources/crystal/api_client_typhoeus_partial.mustache
+++ b/modules/openapi-generator/src/main/resources/crystal/api_client_typhoeus_partial.mustache
@@ -73,7 +73,7 @@
       # set custom cert, if provided
       req_opts[:cainfo] = @config.ssl_ca_cert if @config.ssl_ca_cert
 
-      if [:post, :patch, :put, :delete].include?(http_method)
+      if [:post, :patch, :put, :delete].includes?(http_method)
         req_body = build_request_body(header_params, form_params, opts[:body])
         req_opts.update body: req_body
         if @config.debugging
diff --git a/modules/openapi-generator/src/main/resources/crystal/base_object.mustache b/modules/openapi-generator/src/main/resources/crystal/base_object.mustache
index c7abd09b36b..22dafd41120 100644
--- a/modules/openapi-generator/src/main/resources/crystal/base_object.mustache
+++ b/modules/openapi-generator/src/main/resources/crystal/base_object.mustache
@@ -14,7 +14,7 @@
       super(attributes)
       {{/parent}}
       self.class.openapi_types.each_pair do |key, type|
-        if attributes[self.class.attribute_map[key]].nil? && self.class.openapi_nullable.include?(key)
+        if !attributes[self.class.attribute_map[key]]? && self.class.openapi_nullable.includes?(key)
           self.send("#{key}=", nil)
         elsif type =~ /\AArray<(.*)>/i
           # check to ensure the input is an array given that the attribute
@@ -92,7 +92,7 @@
       self.class.attribute_map.each_pair do |attr, param|
         value = self.send(attr)
         if value.nil?
-          is_nullable = self.class.openapi_nullable.include?(attr)
+          is_nullable = self.class.openapi_nullable.includes?(attr)
           next if !is_nullable || (is_nullable && !instance_variable_defined?(:"@#{attr}"))
         end
 
diff --git a/modules/openapi-generator/src/main/resources/crystal/configuration.mustache b/modules/openapi-generator/src/main/resources/crystal/configuration.mustache
index a3a815fc042..7111ba75e75 100644
--- a/modules/openapi-generator/src/main/resources/crystal/configuration.mustache
+++ b/modules/openapi-generator/src/main/resources/crystal/configuration.mustache
@@ -334,12 +334,12 @@ module {{moduleName}}
       server = servers[index]
       url = server[:url]
 
-      return url unless server.key? :variables
+      return url unless server.has_key? :variables
 
       # go through variable and assign a value
       server[:variables].each do |name, variable|
-        if variables.key?(name)
-          if (!server[:variables][name].key?(:enum_values) || server[:variables][name][:enum_values].include?(variables[name]))
+        if variables.has_key?(name)
+          if (!server[:variables][name].has_key?(:enum_values) || server[:variables][name][:enum_values].includes?(variables[name]))
             url.gsub! "{" + name.to_s + "}", variables[name]
           else
             raise ArgumentError.new("The variable `#{name}` in the server URL has invalid value #{variables[name]}. Must be #{server[:variables][name][:enum_values]}.")
diff --git a/modules/openapi-generator/src/main/resources/crystal/partial_model_generic.mustache b/modules/openapi-generator/src/main/resources/crystal/partial_model_generic.mustache
index 18f00b1d529..c36181c48dc 100644
--- a/modules/openapi-generator/src/main/resources/crystal/partial_model_generic.mustache
+++ b/modules/openapi-generator/src/main/resources/crystal/partial_model_generic.mustache
@@ -30,7 +30,7 @@
       end
 
       def valid?(value)
-        !value || allowable_values.include?(value)
+        !value || allowable_values.includes?(value)
       end
     end
 
@@ -225,7 +225,7 @@
       {{/isNullable}}
       {{#maxLength}}
       if {{^required}}!{{{name}}}.nil? && {{/required}}{{{name}}}.to_s.length > {{{maxLength}}}
-        raise ArgumentError.new("invalid value for "{{{name}}}", the character length must be smaller than or equal to {{{maxLength}}}.")
+        raise ArgumentError.new("invalid value for \"{{{name}}}\", the character length must be smaller than or equal to {{{maxLength}}}.")
       end
 
       {{/maxLength}}
diff --git a/modules/openapi-generator/src/main/resources/crystal/partial_oneof_module.mustache b/modules/openapi-generator/src/main/resources/crystal/partial_oneof_module.mustache
index 14dc1635bb7..18c0a0cffdb 100644
--- a/modules/openapi-generator/src/main/resources/crystal/partial_oneof_module.mustache
+++ b/modules/openapi-generator/src/main/resources/crystal/partial_oneof_module.mustache
@@ -75,7 +75,7 @@
           end
         end
 
-        openapi_one_of.include?(:AnyType) ? data : nil
+        openapi_one_of.includes?(:AnyType) ? data : nil
       {{/discriminator}}
       end
       {{^discriminator}}
diff --git a/samples/client/petstore/crystal/src/petstore/api_client.cr b/samples/client/petstore/crystal/src/petstore/api_client.cr
index b768948f758..4a87147e84d 100644
--- a/samples/client/petstore/crystal/src/petstore/api_client.cr
+++ b/samples/client/petstore/crystal/src/petstore/api_client.cr
@@ -350,7 +350,7 @@ module Petstore
         :verbose => @config.debugging
       }
 
-      if [:post, :patch, :put, :delete].include?(http_method)
+      if [:post, :patch, :put, :delete].includes?(http_method)
         req_body = build_request_body(header_params, form_params, opts[:body])
         req_opts.update body: req_body
         if @config.debugging
diff --git a/samples/client/petstore/crystal/src/petstore/configuration.cr b/samples/client/petstore/crystal/src/petstore/configuration.cr
index 380963045b2..ca837b43ed7 100644
--- a/samples/client/petstore/crystal/src/petstore/configuration.cr
+++ b/samples/client/petstore/crystal/src/petstore/configuration.cr
@@ -249,12 +249,12 @@ module Petstore
       server = servers[index]
       url = server[:url]
 
-      return url unless server.key? :variables
+      return url unless server.has_key? :variables
 
       # go through variable and assign a value
       server[:variables].each do |name, variable|
-        if variables.key?(name)
-          if (!server[:variables][name].key?(:enum_values) || server[:variables][name][:enum_values].include?(variables[name]))
+        if variables.has_key?(name)
+          if (!server[:variables][name].has_key?(:enum_values) || server[:variables][name][:enum_values].includes?(variables[name]))
             url.gsub! "{" + name.to_s + "}", variables[name]
           else
             raise ArgumentError.new("The variable `#{name}` in the server URL has invalid value #{variables[name]}. Must be #{server[:variables][name][:enum_values]}.")
diff --git a/samples/client/petstore/crystal/src/petstore/models/api_response.cr b/samples/client/petstore/crystal/src/petstore/models/api_response.cr
index f6e71542f7e..60c0a64d975 100644
--- a/samples/client/petstore/crystal/src/petstore/models/api_response.cr
+++ b/samples/client/petstore/crystal/src/petstore/models/api_response.cr
@@ -78,7 +78,7 @@ module Petstore
     def build_from_hash(attributes)
       return nil unless attributes.is_a?(Hash)
       self.class.openapi_types.each_pair do |key, type|
-        if attributes[self.class.attribute_map[key]].nil? && self.class.openapi_nullable.include?(key)
+        if !attributes[self.class.attribute_map[key]]? && self.class.openapi_nullable.includes?(key)
           self.send("#{key}=", nil)
         elsif type =~ /\AArray<(.*)>/i
           # check to ensure the input is an array given that the attribute
@@ -156,7 +156,7 @@ module Petstore
       self.class.attribute_map.each_pair do |attr, param|
         value = self.send(attr)
         if value.nil?
-          is_nullable = self.class.openapi_nullable.include?(attr)
+          is_nullable = self.class.openapi_nullable.includes?(attr)
           next if !is_nullable || (is_nullable && !instance_variable_defined?(:"@#{attr}"))
         end
 
diff --git a/samples/client/petstore/crystal/src/petstore/models/category.cr b/samples/client/petstore/crystal/src/petstore/models/category.cr
index 0fab536acb3..33c9acd68cf 100644
--- a/samples/client/petstore/crystal/src/petstore/models/category.cr
+++ b/samples/client/petstore/crystal/src/petstore/models/category.cr
@@ -90,7 +90,7 @@ module Petstore
     def build_from_hash(attributes)
       return nil unless attributes.is_a?(Hash)
       self.class.openapi_types.each_pair do |key, type|
-        if attributes[self.class.attribute_map[key]].nil? && self.class.openapi_nullable.include?(key)
+        if !attributes[self.class.attribute_map[key]]? && self.class.openapi_nullable.includes?(key)
           self.send("#{key}=", nil)
         elsif type =~ /\AArray<(.*)>/i
           # check to ensure the input is an array given that the attribute
@@ -168,7 +168,7 @@ module Petstore
       self.class.attribute_map.each_pair do |attr, param|
         value = self.send(attr)
         if value.nil?
-          is_nullable = self.class.openapi_nullable.include?(attr)
+          is_nullable = self.class.openapi_nullable.includes?(attr)
           next if !is_nullable || (is_nullable && !instance_variable_defined?(:"@#{attr}"))
         end
 
diff --git a/samples/client/petstore/crystal/src/petstore/models/order.cr b/samples/client/petstore/crystal/src/petstore/models/order.cr
index 634d33fdae7..0e036a735c3 100644
--- a/samples/client/petstore/crystal/src/petstore/models/order.cr
+++ b/samples/client/petstore/crystal/src/petstore/models/order.cr
@@ -57,7 +57,7 @@ module Petstore
       end
 
       def valid?(value)
-        !value || allowable_values.include?(value)
+        !value || allowable_values.includes?(value)
       end
     end
 
@@ -129,7 +129,7 @@ module Petstore
     def build_from_hash(attributes)
       return nil unless attributes.is_a?(Hash)
       self.class.openapi_types.each_pair do |key, type|
-        if attributes[self.class.attribute_map[key]].nil? && self.class.openapi_nullable.include?(key)
+        if !attributes[self.class.attribute_map[key]]? && self.class.openapi_nullable.includes?(key)
           self.send("#{key}=", nil)
         elsif type =~ /\AArray<(.*)>/i
           # check to ensure the input is an array given that the attribute
@@ -207,7 +207,7 @@ module Petstore
       self.class.attribute_map.each_pair do |attr, param|
         value = self.send(attr)
         if value.nil?
-          is_nullable = self.class.openapi_nullable.include?(attr)
+          is_nullable = self.class.openapi_nullable.includes?(attr)
           next if !is_nullable || (is_nullable && !instance_variable_defined?(:"@#{attr}"))
         end
 
diff --git a/samples/client/petstore/crystal/src/petstore/models/pet.cr b/samples/client/petstore/crystal/src/petstore/models/pet.cr
index d4431c6aa1e..460ca48c902 100644
--- a/samples/client/petstore/crystal/src/petstore/models/pet.cr
+++ b/samples/client/petstore/crystal/src/petstore/models/pet.cr
@@ -57,7 +57,7 @@ module Petstore
       end
 
       def valid?(value)
-        !value || allowable_values.include?(value)
+        !value || allowable_values.includes?(value)
       end
     end
 
@@ -139,7 +139,7 @@ module Petstore
     def build_from_hash(attributes)
       return nil unless attributes.is_a?(Hash)
       self.class.openapi_types.each_pair do |key, type|
-        if attributes[self.class.attribute_map[key]].nil? && self.class.openapi_nullable.include?(key)
+        if !attributes[self.class.attribute_map[key]]? && self.class.openapi_nullable.includes?(key)
           self.send("#{key}=", nil)
         elsif type =~ /\AArray<(.*)>/i
           # check to ensure the input is an array given that the attribute
@@ -217,7 +217,7 @@ module Petstore
       self.class.attribute_map.each_pair do |attr, param|
         value = self.send(attr)
         if value.nil?
-          is_nullable = self.class.openapi_nullable.include?(attr)
+          is_nullable = self.class.openapi_nullable.includes?(attr)
           next if !is_nullable || (is_nullable && !instance_variable_defined?(:"@#{attr}"))
         end
 
diff --git a/samples/client/petstore/crystal/src/petstore/models/tag.cr b/samples/client/petstore/crystal/src/petstore/models/tag.cr
index fa2968a9035..d377ddcdf74 100644
--- a/samples/client/petstore/crystal/src/petstore/models/tag.cr
+++ b/samples/client/petstore/crystal/src/petstore/models/tag.cr
@@ -73,7 +73,7 @@ module Petstore
     def build_from_hash(attributes)
       return nil unless attributes.is_a?(Hash)
       self.class.openapi_types.each_pair do |key, type|
-        if attributes[self.class.attribute_map[key]].nil? && self.class.openapi_nullable.include?(key)
+        if !attributes[self.class.attribute_map[key]]? && self.class.openapi_nullable.includes?(key)
           self.send("#{key}=", nil)
         elsif type =~ /\AArray<(.*)>/i
           # check to ensure the input is an array given that the attribute
@@ -151,7 +151,7 @@ module Petstore
       self.class.attribute_map.each_pair do |attr, param|
         value = self.send(attr)
         if value.nil?
-          is_nullable = self.class.openapi_nullable.include?(attr)
+          is_nullable = self.class.openapi_nullable.includes?(attr)
           next if !is_nullable || (is_nullable && !instance_variable_defined?(:"@#{attr}"))
         end
 
diff --git a/samples/client/petstore/crystal/src/petstore/models/user.cr b/samples/client/petstore/crystal/src/petstore/models/user.cr
index d3922e82394..5794e52d4f0 100644
--- a/samples/client/petstore/crystal/src/petstore/models/user.cr
+++ b/samples/client/petstore/crystal/src/petstore/models/user.cr
@@ -104,7 +104,7 @@ module Petstore
     def build_from_hash(attributes)
       return nil unless attributes.is_a?(Hash)
       self.class.openapi_types.each_pair do |key, type|
-        if attributes[self.class.attribute_map[key]].nil? && self.class.openapi_nullable.include?(key)
+        if !attributes[self.class.attribute_map[key]]? && self.class.openapi_nullable.includes?(key)
           self.send("#{key}=", nil)
         elsif type =~ /\AArray<(.*)>/i
           # check to ensure the input is an array given that the attribute
@@ -182,7 +182,7 @@ module Petstore
       self.class.attribute_map.each_pair do |attr, param|
         value = self.send(attr)
         if value.nil?
-          is_nullable = self.class.openapi_nullable.include?(attr)
+          is_nullable = self.class.openapi_nullable.includes?(attr)
           next if !is_nullable || (is_nullable && !instance_variable_defined?(:"@#{attr}"))
         end