Fix noisy diagnostic on PR's relating to f# nullable check

tests/authoring/Applicability/AppliesToFrontMatter.fs

@@ -24,7 +24,7 @@ applies_to:
 """
     [<Fact>]
     let ``apply matches expected`` () =
-        markdown |> appliesTo (Unchecked.defaultof<ApplicableTo>)
+        markdown |> appliesTo Unchecked.defaultof<ApplicableTo>
 
 type ``apply default to top level arguments`` () =
     static let markdown = frontMatter """
@@ -212,7 +212,7 @@ applies_to:
 """
     [<Fact>]
     let ``does not render label`` () =
-        markdown |> appliesTo (Unchecked.defaultof<ApplicableTo>)
+        markdown |> appliesTo Unchecked.defaultof<ApplicableTo>
 
 type ``parses applies_to with multiple categories in any order`` () =
     static let markdown = frontMatter """

tests/authoring/Framework/MarkdownDocumentAssertions.fs

@@ -27,17 +27,19 @@
         unsupportedBlocks
 
     [<DebuggerStepThrough>]
-    let appliesTo (expectedAvailability: ApplicableTo) (actual: Lazy<GeneratorResults>) =
+    let appliesTo (expectedAvailability: ApplicableTo | null) (actual: Lazy<GeneratorResults>) =
         let actual = actual.Value
         let result = actual.MarkdownResults |> Seq.find (fun r -> r.File.RelativePath = "index.md")
         let matter = result.File.YamlFrontMatter
         match matter with
         | NonNull m ->
-            if expectedAvailability <> null then
-                m.AppliesTo.Diagnostics <- expectedAvailability.Diagnostics
+            match expectedAvailability with
+            | NonNull a -> m.AppliesTo.Diagnostics <- a.Diagnostics
+            | _ -> ()
+
             let apply = m.AppliesTo
             test <@ apply = expectedAvailability @>
-        | _ -> failwithf "%s has no yamlfront matter" result.File.RelativePath
+        | _ -> failwithf $"%s{result.File.RelativePath} has no yamlfront matter"
 
 
     [<DebuggerStepThrough>]