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UnrealBuildTool fails with null argument

After upgrading my project to 4.17 it's started occasionally failing to compile because UnrealBuildTool encounters a System.ArgumentNullException when it tries to run. The full callstack is:

 2>EXEC : error : System.ArgumentNullException: Value cannot be null.
 2>  Parameter name: source
 2>     at System.Linq.Enumerable.Any[TSource](IEnumerable`1 source, Func`2 predicate)
 2>     at UnrealBuildTool.ExternalExecution.ExecuteHeaderToolIfNecessary(BuildConfiguration BuildConfiguration, UEBuildTarget Target, CppCompileEnvironment GlobalCompileEnvironment, List`1 UObjectModules, FileReference ModuleInfoFileName, ECompilationResult& UHTResult)
 2>     at UnrealBuildTool.UnrealBuildTool.RunUBT(BuildConfiguration BuildConfiguration, String[] Arguments, FileReference ProjectFile)

I don't recall encountering this error while testing the preview but that may have simply been luck since I didn't do more than occasionally make sure all my code still compiled and ran. Doing a full rebuild of my project fixes the error but I'd like to avoid having to do that if possible since it usually takes a few minutes.

Product Version: UE 4.17
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asked Aug 08 '17 at 04:19 PM in Bug Reports

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avatar image kgamble Aug 08 '17 at 08:02 PM

Further testing finds that this only occurs when I change a header file. I made a new (blank) code project and encounter the exact same issue and tried it on a different machine so it doesn't seem to be an issue with either my project or computer.

avatar image RoyAwesome Aug 09 '17 at 02:22 AM

I'm also having this issue when changing a header.

avatar image Gnometech Aug 11 '17 at 03:20 PM

Adding my own voice to this. Added two transient properties to a class header, and was hit by this exact build error. Clean and rebuild got me past it.

avatar image Büke Sep 23 '17 at 06:58 AM

Same error, when changing a .h file with UE 4.18p1.

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2 answers: sort voted first

Have you tried this fix by Ben Marsh from Epic?

I was facing similar issue,this has solved my problem.

I hope that,it helps you.

Link to forum post by Ben

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answered Aug 11 '17 at 05:59 PM

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avatar image kgamble Aug 11 '17 at 06:17 PM

Yep, that did it. Didn't think to check that part of the forums so thanks for the link.

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It's not a fix, but if you regenerate project files you can compile again.

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answered Aug 09 '17 at 03:29 AM

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avatar image DaGaffer Aug 09 '17 at 08:27 PM

I'm having the same issue.

The workaround I've used is to Rebuild/build clean - works as well.

avatar image ZABBA_THE_HUT Aug 10 '17 at 12:24 PM

I have the same issue after updating to 4.17. I can confirm that both workarounds work, but it is quite cumbersome and time consuming to rebuild every time.


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