[jira] [Created] (THRIFT-5238) GetHashCode can throw NullReferenceException

[Lewis Jackson (Jira)]

Lewis Jackson created THRIFT-5238:
-------------------------------------

             Summary: GetHashCode can throw NullReferenceException
                 Key: THRIFT-5238
                 URL: https://issues.apache.org/jira/browse/THRIFT-5238
             Project: Thrift
          Issue Type: Bug
          Components: netstd - Compiler
    Affects Versions: 0.13.0
         Environment: OS: Windows 10 Pro Version 1903 Build 18362.900

 
            Reporter: Lewis Jackson
         Attachments: Thrift-NullReferenceException-master.zip

Thrift generates a setter for each field like this:

{code:c#}
    public string WebhooksSecret
    {
      get
      {
        return _WebhooksSecret;
      }
      set
      {
        __isset.WebhooksSecret = true;
        this._WebhooksSecret = value;
      }
    }
{code}

But if you set the field to _null_, it will be marked as set in the _isset_ 
dictionary. Thrift also overrides _GetHashCode()_ like this:

{code:c#}
    public override int GetHashCode() {
      int hashcode = 157;
      unchecked {
        if(__isset.Url)
          hashcode = (hashcode * 397) + Url.GetHashCode();
        if(__isset.WebhooksSecret)
          hashcode = (hashcode * 397) + WebhooksSecret.GetHashCode();
        if(__isset.Username)
          hashcode = (hashcode * 397) + Username.GetHashCode();
        if(__isset.WebhooksTypes)
          hashcode = (hashcode * 397) + TCollections.GetHashCode(WebhooksTypes);
      }
      return hashcode;
    }
{code}

Note that it doesn't protect against _null_, where other overrides like 
_ToString()_ do:

{code:c#}
    public override string ToString()
    {
//...
      if (WebhooksSecret != null && __isset.WebhooksSecret)
      {
        if(!__first) { sb.Append(", "); }
        __first = false;
        sb.Append("WebhooksSecret: ");
        sb.Append(WebhooksSecret);
      }
//...
    }
{code}

This can result in the field being set to _null_ then throwing a 
_NullReferenceException_ if a consumer calls _GetHashCode()_.

I've attached a repro in the fro



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