Process OLE Objects parallel

Hi Team!

We are trying to process embedded documents in parallel and there are some exception during the processing. I attached the sample files and the project so you can reproduce it. Please try it more that once because the exceptions not always have been thrown.

This is one of the exception when we trying to save the embedded ppt to a Memory Stream as a ppt:

System.AggregateException: One or more errors occurred. (Object reference not set to an instance of an object.)
---> System.NullReferenceException: Object reference not set to an instance of an object.
at Aspose.Slides.GradientFormat.(IGradientFormat )
at   .(ILineFillFormat )
at   .(ILineFillFormat )
at Aspose.Slides.LineFillFormat.(ILineFillFormat )
at ​  .(ILineFormat )
at ​  .(ILineFormat )
at Aspose.Slides.LineFormat.(ILineFormat )
at    .      (IBasePortionFormat )
at    .      (IBasePortionFormat )
at Aspose.Slides.BasePortionFormat.(IBasePortionFormat )
at    .(IShape ,     )
at    .    )
at         ()
at ​  .(    )
at ​  .(    )
at ​  .(    )
at    .(    )
at    . ()
at    .()
at    .(Stream , ISaveOptions )
at Aspose.Slides.Presentation.Save(Stream stream, SaveFormat format, ISaveOptions options)
at Aspose.Slides.Presentation.Save(Stream stream, SaveFormat format)

Another one is coming from the Presentation constructor:

System.AggregateException: One or more errors occurred. (Object reference not set to an instance of an object.) (Object reference not set to an instance of an object.) (Object reference not set to an instance of an object.)
 ---> System.NullReferenceException: Object reference not set to an instance of an object.
   at    .Equals(Object )
   at    .Equals(Object )
   at Aspose.Slides.PVIObject.Equals(Object obj)
   at   .(IPortionFormat ,  ,     )
   at    .(IParagraphFormat ,  ,     )
   at    .(IParagraphCollection ,  ,     )
   at    .(ITextFrame ,     ,     )
   at    .(ITextFrame ,  ,     )
   at​  .(IAutoShape ,     ,     ,   )
   at    .(IShape ,     ,     ,   )
   at    .(IShapeCollection , IShape , ShapeFrame )
   at Aspose.Slides.ShapeCollection.AddClone(IShape sourceShape)
   at    .(    , LayoutSlide )
   at    .    )
   at    . ()
   at    .(    , InterruptionToken )
   at Aspose.Slides.Presentation.(    )
   at Aspose.Slides.Presentation.(Stream , Boolean )
   at Aspose.Slides.Presentation.(Stream )
   at Aspose.Slides.Presentation..ctor(Stream stream)

Sample files:
test_files.zip (930.2 KB)

Project:
ProcessOleObjectParallel.zip (3.6 KB)

Aspose.Slides 21.02
.Net Core 3.1
Linux environment

@erdeiga,
Thank you for the issue description. I have reproduced the problem and got the same results. I have logged the issue in our tracking system with ID SLIDESNET-42445. Our development team will investigate it. You will be notified when it is fixed.