Fixed null exception

Author: ncave

fcs/FSharp.Compiler.Service/service_slim.fs

@@ -60,6 +60,7 @@ type InteractiveChecker internal (tcConfig, tcGlobals, tcImports, tcInitialState
     static member Create(projectOptions: FSharpProjectOptions) =
         let tcConfig =
             let tcConfigB = TcConfigBuilder.Initial
+            tcConfigB.legacyReferenceResolver <- SimulatedMSBuildReferenceResolver.SimulatedMSBuildResolver
             let sourceFiles = projectOptions.SourceFiles |> Array.toList
             let argv = projectOptions.OtherOptions |> Array.toList
             let _sourceFiles = ApplyCommandLineArgs(tcConfigB, sourceFiles, argv)