Use IsNil instead of .Length (dotnet#9337)

Author: forki

src/fsharp/IlxGen.fs

@@ -7645,7 +7645,7 @@ let CodegenAssembly cenv eenv mgbuf fileImpls =
         // top-level initialization code.
         let extraBindings = mgbuf.GrabExtraBindingsToGenerate()
         //printfn "#extraBindings = %d" extraBindings.Length
-        if extraBindings.Length > 0 then
+        if not (isNil extraBindings) then
             let mexpr = TMDefs [ for b in extraBindings -> TMDefLet(b, range0) ]
             let _emptyTopInstrs, _emptyTopCode =
                 CodeGenMethod cenv mgbuf ([], "unused", eenv, 0, (fun cgbuf eenv ->

src/fsharp/TypedTreeOps.fs

@@ -3887,8 +3887,8 @@ module DebugPrint =
 
     and appL g flayout tys args =
         let z = flayout
-        let z = if tys.Length > 0 then z ^^ instL typeL tys else z
-        let z = if args.Length > 0 then z --- spaceListL (List.map (atomL g) args) else z
+        let z = if isNil tys then z else z ^^ instL typeL tys
+        let z = if isNil args then z else z --- spaceListL (List.map (atomL g) args)
         z
 
     and implFileL g (TImplFile (_, _, mexpr, _, _, _)) =

src/fsharp/fsi/fsi.fs

@@ -1479,7 +1479,7 @@ type internal FsiDynamicCompiler
                             for folder in result.Roots do
                                 tcConfigB.AddIncludePath(m, folder, "")
                             let scripts = result.SourceFiles |> Seq.toList
-                            if scripts |> Seq.length > 0 then
+                            if not (isNil scripts) then
                                 fsiDynamicCompiler.EvalSourceFiles(ctok, istate, m, scripts, lexResourceManager, errorLogger)
                             else istate
                     with _ ->

src/fsharp/service/ServiceAnalysis.fs

@@ -181,7 +181,7 @@ module UnusedOpens =
                 | true, scopes -> openStatement.AppliedScope :: scopes
                 | _ -> [openStatement.AppliedScope]
             usedModules.[openedModule.Entity] <- scopes
-        newlyOpenedModules.Length > 0
+        not (isNil newlyOpenedModules)
 
     /// Incrementally filter out the open statements one by one. Filter those whose contents are referred to somewhere in the symbol uses.
     /// Async to allow cancellation.