[c-sharp-operations] not handling interface as return type

[PeterEeg]

Describe the bug

There seems to be an issue with the c-sharp-operations plug-in when trying to generate code for a query which returns an interface.

Using the live demo I'm getting the error message: "Cannot read properties of undefined (reading 'fields')"

Schema:

type Query {
  sampleQuery: [IMyReturnType!]!
}

interface IMyReturnType {
  id: ID!
}

type MyReturnType implements IMyReturnType {
  id: ID!
}

Operations:

query GetSampleQuery {
  sampleQuery {
    id
  }
}

codegen.yml:

generates:
  src/main/c-sharp/my-org/my-app/Types.cs:
    plugins:
      - c-sharp-operations
    config:
      typesafeOperation: true

Your Example Website or App

Steps to Reproduce the Bug or Issue

Use the live demo (https://www.graphql-code-generator.com/) with the supplied schema and operations.

Expected behavior

I would expect the result to be similar to the result if the query returned MyReturnType e.g.:

using System;
using Newtonsoft.Json;
using GraphQL;
using GraphQL.Client.Abstractions;

namespace GraphQLCodeGen {

    public class GetSampleQueryGQL {
      /// <summary>
      /// GetSampleQueryGQL.Request 
      /// </summary>
      public static GraphQLRequest Request() {
        return new GraphQLRequest {
          Query = GetSampleQueryDocument,
          OperationName = "GetSampleQuery"
        };
      }

      /// <remarks>This method is obsolete. Use Request instead.</remarks>
      public static GraphQLRequest getGetSampleQueryGQL() {
        return Request();
      }
      
      public static string GetSampleQueryDocument = @"
        query GetSampleQuery {
          sampleQuery {
            id
          }
        }
        ";
            
      
      public class Response {
      
        public class MyReturnTypeSelection {
        
          [JsonProperty("id")]
          public string id { get; set; }
          
        }
        
        [JsonProperty("sampleQuery")]
        public MyReturnTypeSelection sampleQuery { get; set; }
        
      }
      
      public static System.Threading.Tasks.Task<GraphQLResponse<Response>> SendQueryAsync(IGraphQLClient client, System.Threading.CancellationToken cancellationToken = default) {
        return client.SendQueryAsync<Response>(Request(), cancellationToken);
      }
      
    } 
}

Screenshots or Videos

Platform

• @graphql-codegen/* version: 2.7.0

Codegen Config File

No response

Additional context

No response