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Value cannot be null. Parameter name: output

GroupDocs.Conversion Product Family
#1

I am trying to convert a pdf into a ppt, but am getting this error. It doesn’t tell me much besides that.
Value cannot be null.
Parameter name: output
group-docs.jpg (64.1 KB)

This is the Json Response:
{"data":{"Message":"An error has occurred.","ExceptionMessage":"Value cannot be null.\r\nParameter name: output","ExceptionType":"GroupDocs.Conversion.Exceptions.GroupDocsConversionException","StackTrace":" at GroupDocs.Conversion.Converter.Convert(SaveDocumentStreamForFileType document, ConvertedDocumentStream documentCompleted, ConvertOptionsProvider convertOptionsProvider)\r\n at MotivUmbraco.Services.FileConverterService.<Convert>d__6.MoveNext() in C:\\MotivSolution\\Code\\MotivUmbracoV8\\Services\\FileConverterService.cs:line 34\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Runtime.CompilerServices.TaskAwaiter1.GetResult()\r\n at MotivUmbraco.Controllers.MicrositeApiController.d__2.MoveNext() in C:\MotivSolution\Code\MotivUmbracoV8\Controllers\MicrositeApiController.cs:line 38\r\n— End of stack trace from previous location where exception was thrown —\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Threading.Tasks.TaskHelpersExtensions.d__11.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__1.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__3.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__15.MoveNext()"},"status":500,"config":{"method":"POST","transformRequest":[null],"transformResponse":[null],"jsonpCallbackParam":"callback","url":"/umbraco/api/MicrositeApi/ConvertToPpt","data":{},"headers":{"Accept":"application/json, text/plain, */*"}},"statusText":"Internal Server Error","xhrStatus":"complete"}

This is the class
`using GroupDocs.Conversion;
using GroupDocs.Conversion.Contracts;
using System.Diagnostics;
using System.IO;
using System.Threading.Tasks;

public class FileConverterService
{
    private readonly Stream _stream;
    public Stream OutputStream { get; private set; }
    public FileConverterService(Stream stream)
    {
        this._stream = stream;
    }
    public async Task<Stream> Convert(string licensePath)
    {
        using (Converter converter = new Converter(GetFileStream))
        {
            License license = new License();
            license.SetLicense(licensePath);
            PossibleConversions conversions = converter.GetPossibleConversions();
            SaveDocumentStream save = new SaveDocumentStream(SetOutputStream);
            var convertOptions = converter.GetPossibleConversions()["ppt"].ConvertOptions;

            try
            {
                converter.Convert(save, convertOptions);
            }
            catch (System.Exception ex)
            {
                Debug.WriteLine(ex.Message);
                throw;
            }
            await Task.FromResult(true);
            return OutputStream;
        }
    }
    private Stream GetFileStream() => _stream;

    private Stream SetOutputStream() => OutputStream;
}`

I do have a temporary license applied

What am I doing wrong?

#2

@ccasalicchio

Please share following details:

  • API version that you are using (e.g. 20.5, 20.9)
  • Problematic PDF file
  • A simple console application (if possible) using that issue could be reproduced
#3

Actually, I was able to get it to save to the local disk G:\test.ppt so the pdf is ok.

The final app will open a new browser tab and download the powerpoint file, without saving it to the server’s hard disk. So I need to save the converted file as a stream, so I can push it to the browser. Is that possible? I couldn’t find any examples in the documentation

id=“GroupDocs.Conversion” version=“20.11.0” targetFramework=“net472”

Here’s the code snippet

    using GroupDocs.Conversion;
    using GroupDocs.Conversion.Contracts;
    using System.Diagnostics;
    using System.IO;
    using System.Threading.Tasks;

    public class FileConverterService
    {
        private readonly Stream _stream;
        public Stream OutputStream { get; private set; }
        public FileConverterService(Stream stream)
        {
            this._stream = stream;
        }
        public async Task<Stream> Convert(string licensePath)
        {
            using (Converter converter = new Converter(GetFileStream))
            {
                License license = new License();
                license.SetLicense(licensePath);
                PossibleConversions conversions = converter.GetPossibleConversions();
                SaveDocumentStream save = new SaveDocumentStream(SetOutputStream);
                var convertOptions = converter.GetPossibleConversions()["ppt"].ConvertOptions;

                try
                {
                    converter.Convert("G:\\test.ppt", convertOptions); 
                    //converter.Convert(save, convertOptions);
                }
                catch (System.Exception ex)
                {
                    Debug.WriteLine(ex.Message);
                    throw;
                }
                await Task.FromResult(true);
                return OutputStream;
            }
        }
        private Stream GetFileStream() => _stream;

        private Stream SetOutputStream() => OutputStream;
    }
#4

@ccasalicchio

Please have a look at the code below:

var source = "source file";
using (var resultStream = new MemoryStream())
{
    using (var converter = new Converter(source))
    {
       //converting source file to PDF
        var options = new PdfConvertOptions();
        converter.Convert(() => new MemoryStream(), convertedStream => convertedStream.CopyTo(resultStream), options);
    }
}

You can save the result in memory stream. Let us know if it’ll help.

#5

Great, I got it working. Thank you!

Now, is there a way to embed custom fonts into the power point file? Since the PDF uses Open Sans (Google fonts) but when opening in a computer without it installed, the power points looks ugly.

#6

@ccasalicchio

You can set default font or substitute a font, please take a look at this API reference guide. Let us know if it helps.

#7

Is there a way to use a pre-existing ppt that has the font embedded?

#8

@ccasalicchio

Could you please further elaborate this?

#9

Nevermind the previous question. I’ve tried setting Verdana as a Substitute font but it doesn’t appear to be doing anything. How can I confirm this?

    using GroupDocs.Conversion;
    using GroupDocs.Conversion.Contracts;
    using GroupDocs.Conversion.FileTypes;
    using GroupDocs.Conversion.Options.Load;
    using System.Collections.Generic;
    using System.IO;
    using System.Threading.Tasks;
    public class FileConverterService
    {
        private readonly Stream _stream;
        public FileConverterService(Stream stream)
        {
            this._stream = stream;
        }
        public async Task<MemoryStream> Convert(string licensePath)
        {
            var resultStream = new MemoryStream();

            License license = new License();
            license.SetLicense(licensePath);
            LoadOptions getLoadOptions() => new PresentationLoadOptions
            {
                DefaultFont = "Open Sans",
              
                Format = PresentationFileType.Pptx,
                FontSubstitutes = new List<FontSubstitute>
                {
                    
                    FontSubstitute.Create("Open Sans","Verdana")
                }
            };

            using (var converter = new Converter(GetFileStream, getLoadOptions))
            {
                var options = converter.GetPossibleConversions()["pptx"].ConvertOptions;
                converter.Convert(() => new MemoryStream(), convertedStream => convertedStream.CopyTo(resultStream), options);
            }
            await Task.FromResult(true);
            return resultStream;
        }
        private Stream GetFileStream() => _stream;
    }

I’ve also tried changing the PDF font to Verdana, but now the conversion fails with this error:

"ExceptionMessage":"Object reference not set to an instance of an object.","ExceptionType":"GroupDocs.Conversion.Exceptions.GroupDocsConversionException","StackTrace":" at GroupDocs.Conversion.Converter.Convert(SaveDocumentStreamForFileType document, ConvertedDocumentStream documentCompleted, ConvertOptionsProvider convertOptionsProvider)\r\n at MotivUmbraco.Services.FileConverterService.<Convert>d__2.MoveNext() in C:\\MotivSolution\\Code\\MotivUmbracoV8\\Services\\FileConverterService.cs:line 38\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Runtime.CompilerServices.TaskAwaiter1.GetResult()\r\n at MotivUmbraco.Controllers.MicrositeApiController.d__2.MoveNext() in C:\MotivSolution\Code\MotivUmbracoV8\Controllers\MicrositeApiController.cs:line 34\r\n— End of stack trace from previous location where exception was thrown —\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Threading.Tasks.TaskHelpersExtensions.d__11.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Web.Http.Controllers.ApiControllerActionInvoker.<InvokeActionAsyncCore>d__1.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Web.Http.Controllers.ActionFilterResult.<ExecuteAsync>d__5.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Web.Http.Filters.AuthorizationFilterAttribute.<ExecuteAuthorizationFilterAsyncCore>d__3.MoveNext()\r\n--- End of stack trace from previous location where exception was thrown ---\r\n at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()\r\n at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)\r\n at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__15.MoveNext()"

I’m not sure what is wrong now

#10

@ccasalicchio

We’re investigating this issue. Your investigation ticket ID is CONVERSIONNET-4336. You’ll be notified as there’s any update.

#11

I have another issue with conversion. In the pdf, the text renders correctly
image.png (12.4 KB)

But the ppt renders with a weird symbol. How can I fix this?
image.png (9.7 KB)

#12

@ccasalicchio

Please share the problematic/source file and we’ll look into this issue.

#13

Here you go. files.zip (2.7 MB)

#14

@ccasalicchio

We’re investigating this issue. Your investigation ticket ID is CONVERSIONNET-4372. We’ll notify you in case of any update.

#15

Hi Guys, any news on this? Pete Kuhtey, from MotivIndex [pete@motivindex.com] (mailto:pete@motivindex.com) has purchased a full license (I’m developing it for them).

#16

@ccasalicchio

CONVERSIONNET-4372 is expected to be fixed in API version/release 21.1. As far as CONVERSIONNET-4336 is concerned, we did some changes in the code and it worked for us (for PDF case).

Conversion.Options.Load.LoadOptions getLoadOptions() => new PdfLoadOptions
{
    DefaultFont = "Open Sans",

    FontSubstitutes = new List<FontSubstitute>
    {
        FontSubstitute.Create("Algerian","Verdana")
    }
};
using (Converter converter = new Converter("test.pdf", getLoadOptions))
{
    PresentationConvertOptions options = new PresentationConvertOptions();
    converter.Convert("output.pptx", options);
}

LoadOptions should be PdfLoadOptions in case of PDF. Please let us know if your issue is fixed this way.