Null Reference Exception generating client

AutoRest fails to generate a client for the following swagger (refs point to documents on an internal server):

{
  "swagger": "2.0",
  "info": {
    "title": "Bug Example",
    "description": "A summary of a a bug",
    "version": "01.00.00"
  },
  "schemes": [
    "https"
  ],
  "consumes": [
    "application/json"
  ],
  "produces": [
    "application/json"
  ],
  "paths": {
    "/a/path": {
      "get": {
        "operationId": "getAPath",
        "description": "a path",
        "responses": {
          "200": {
            "description": "A positive response",
            "schema": {
              "$ref": "#/definitions/aModel"
            }
          },
          "401": {
            "$ref": "http://internalserver/api-governance/shared/responses/401.json"
          },
          "404": {
            "$ref": "http://internalserver/api-governance/shared/responses/404.json"
          }
        }
      }
    }
  },
  "definitions": {
    "aModel": {
      "type": "object",
      "title": "someModel",
      "description": "Representation for a model",
      "properties": {
        "data": {
          "type": "object",
          "properties": {
            "aModel": {
              "type": "array",
              "items": {
                "type": "object",
                "allOf": [
                  {
                    "$ref": "#/definitions/aModelAttributes"
                  }
                ]
              }
            }
          }
        },
        "meta": {
          "type": "object",
          "description": "The metadata for the resource",
          "allOf": [
            {
              "$ref": "http://internalserver/api-governance/shared/definitions/pagination-meta.json"
            }
          ]
        }
      }
    },
    "aModelAttributes": {
      "properties": {
        "prop1": {
          "type": "string"
        }
      }
    }
  }
}

The stack trace is:

Code generation failed.
AutoRest.exe -namespace MyNamespace -CodeGenerator CSharp -Input .\example.json -verbose
error: [FATAL] Error generating client model: Object reference not set to an instance of an object.
System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.Rest.Modeler.Swagger.JsonConverters.ResponseRefConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateDictionary(IDictionary dictionary, JsonReader reader, JsonDictionaryContract contract, JsonProperty containerPrope
rty, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract contain
erContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract
containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue(JsonProperty property, JsonConverter propertyConverter, JsonContainerContract containerContract, JsonProp
erty containerProperty, JsonReader reader, Object target)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract contain
erContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract
containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateDictionary(IDictionary dictionary, JsonReader reader, JsonDictionaryContract contract, JsonProperty containerPrope
rty, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract contain
erContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract
containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)
   at Microsoft.Rest.Modeler.Swagger.JsonConverters.PathLevelParameterConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)
   at Microsoft.Rest.Modeler.Swagger.JsonConverters.PathItemRefConverter.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateDictionary(IDictionary dictionary, JsonReader reader, JsonDictionaryContract contract, JsonProperty containerPrope
rty, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract contain
erContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract
containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue(JsonProperty property, JsonConverter propertyConverter, JsonContainerContract containerContract, JsonProp
erty containerProperty, JsonReader reader, Object target)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateObject(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract contain
erContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract
containerContract, JsonProperty containerMember, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonConvert.DeserializeObject(String value, Type type, JsonSerializerSettings settings)
   at Newtonsoft.Json.JsonConvert.DeserializeObject[T](String value, JsonSerializerSettings settings)
   at Microsoft.Rest.Modeler.Swagger.SwaggerParser.Parse(String swaggerDocument)
   at Microsoft.Rest.Modeler.Swagger.SwaggerParser.Load(String path, IFileSystem fileSystem)
   at Microsoft.Rest.Modeler.Swagger.SwaggerModeler.Build()
   at Microsoft.Rest.Generator.AutoRest.Generate(Settings settings)
INFO: AutoRest Core 0.16.0.0
INFO: Initializing modeler.
INFO: Initializing modeler.
INFO: Parsing swagger json file.

If the error response definitions are removed (like so):

{
  "swagger": "2.0",
  "info": {
    "title": "Bug Example",
    "description": "A summary of a a bug",
    "version": "01.00.00"
  },
  "schemes": [
    "https"
  ],
  "consumes": [
    "application/json"
  ],
  "produces": [
    "application/json"
  ],
  "paths": {
    "/a/path": {
      "get": {
        "operationId": "getAPath",
        "description": "a path",
        "responses": {
          "200": {
            "description": "A positive response",
            "schema": {
              "$ref": "#/definitions/aModel"
            }
          }
        }
      }
    }
  },
  "definitions": {
    "aModel": {
      "type": "object",
      "title": "someModel",
      "description": "Representation for a model",
      "properties": {
        "data": {
          "type": "object",
          "properties": {
            "aModel": {
              "type": "array",
              "items": {
                "type": "object",
                "allOf": [
                  {
                    "$ref": "#/definitions/aModelAttributes"
                  }
                ]
              }
            }
          }
        },
        "meta": {
          "type": "object",
          "description": "The metadata for the resource",
          "allOf": [
            {
              "$ref": "http://internalserver/api-governance/shared/definitions/pagination-meta.json"
            }
          ]
        }
      }
    },
    "aModelAttributes": {
      "properties": {
        "prop1": {
          "type": "string"
        }
      }
    }
  }
}

Then I get:

Code generation failed.
AutoRest.exe -namespace MyNamespace -CodeGenerator CSharp -Input .\example.json -verbose
error: [FATAL] Error generating client model: The given key was not present in the dictionary.
System.Collections.Generic.KeyNotFoundException: The given key was not present in the dictionary.
   at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
   at Microsoft.Rest.Modeler.Swagger.SwaggerModeler.Build()
   at Microsoft.Rest.Generator.AutoRest.Generate(Settings settings)
INFO: AutoRest Core 0.16.0.0
INFO: Initializing modeler.
INFO: Initializing modeler.
INFO: Parsing swagger json file.
INFO: Generating client model from swagger model.

If I remove any refs that point to external documents, then the client object model is generated successfully.

[olydis]

Absolutely correct. Looking at your examples again, it seems I was drawing the wrong conclusions from the discussion… your Swagger is perfectly fine 👍 but using the current AutoRest, both of your examples work for me (after pointing the external URLs to some files/URLs that are accessible)!

Do you have a counterexample (with URLs that work for me - or post the referenced swagger)? 😃

[Osipion]

@olydis Looks like $refs can be used other than to reference schemas although I don’t know if that includes my example. The spec seems a little confusing on where $ref may be used - from what I can work out:

1. To point to a definition schema
2. Within a definition schema to point to a sub schema
3. To point to a Path Object definition
4. “To reference parameters and responses that are defined at the top level” - not sure what “top level” means here, but sounds like I can use $ref to point to a response definition, which was my problem.

The spec also says:

parts of the definitions can be split into separate files, at the discretion of the user. This is applicable for $ref fields in the specification as follows from the JSON Schema definitions

Which suggests a relatively arbitrary use of JSON refs is supported, and the official swagger editor allows it.

I guess the problem would be that it’s difficult to work out what the error is when AutoRest rejects it since other swagger tooling doesn’t highlight it. Would a better exception message be possible?