You may see the following error message while saving an analysis file to the library. 

Error message: Could not publish Dashboard.

NullReferenceException at Spotfire.Dxp.Data:
Object reference not set to an instance of an object. (HRESULT: 80004003)

Stack Trace:
   at Spotfire.Dxp.Data.InformationModel.Parameter.AddLibraryDependencies(HashSet`1 dependencies)
   at Spotfire.Dxp.Data.InformationModel.InformationLinkElement.AddLibraryDependencies(HashSet`1 dependencies)
   at Spotfire.Dxp.Data.Import.InformationLinkDataSource.GetLibraryDependencies()
   at Spotfire.Dxp.Data.DataFlow.GetLibraryDependencies()
   at Spotfire.Dxp.Application.AnalysisApplication.AddDependencies(LibraryEntry entry, Document document)
   at Spotfire.Dxp.Application.AnalysisApplication.SaveAs(LibraryEntry entry, Document document, LibraryItemMetadataSettings metadataSettings, DocumentSaveSettings saveSettings)
   at Spotfire.Dxp.Forms.Application.FileUserActions.<>c__DisplayClass44_0.<SaveAsLibrary>b__0()
   at Spotfire.Dxp.Forms.Application.FormsProgressService.ProgressThread.DoOperationLoop()
 

The above error is seen if the Information Link associated to that specific file is either corrupted or not saved to the library. Here are few possible solutions:

1) Check if the Information Link has GUID mentioned in the Source Information of the analysis. If there is no GUID of Information Link then that clearly indicates that it is not saved to the library. See below for your reference:

2) Create the corrupted Information Link from scratch if the dxp is corrupted 
 

This Knowledge Base Article provides you list of steps to follow when you cannot publish an analysis file to the library via Spotfire Analyst.