simplify null check

Author: smdn

src/Smdn.Reflection.ReverseGenerating.ListApi/Smdn.Reflection.ReverseGenerating.ListApi.Build/MSBuildExePath.cs

@@ -83,11 +83,7 @@ private static string GetMSBuildExePath(out string? sdkVersion)
 #if true
     sdkVersion = default;
 
-    var sdkBasePath = GetSdkBasePath(out sdkVersion);
-
-    if (sdkBasePath is null)
-      throw new InvalidOperationException("could not get SDK base path");
-
+    var sdkBasePath = GetSdkBasePath(out sdkVersion) ?? throw new InvalidOperationException("could not get SDK base path");
     var msbuildExePath = JoinPath(
       sdkBasePath,
       "MSBuild.dll" // .NET SDK always ships MSBuild executables with the extension 'dll'

src/Smdn.Reflection.ReverseGenerating.ListApi/Smdn.Reflection.ReverseGenerating.ListApi/ProjectFinder.cs

@@ -32,10 +32,8 @@ public static FileInfo FindSingleProjectOrSolution(
     if (1 < solutionAndProjectFiles.Count())
       throw new InvalidOperationException($"multiple solution or project file found in directory '{directory.FullName}'");
 
-    var first = solutionAndProjectFiles.FirstOrDefault();
-
-    if (first is null)
-      throw new FileNotFoundException($"no solution or project file found in directory '{directory.FullName}'");
+    var first = solutionAndProjectFiles.FirstOrDefault()
+      ?? throw new FileNotFoundException($"no solution or project file found in directory '{directory.FullName}'");
 
     logger?.LogDebug("found '{ProjectOrSolutionPath}'", first.FullName);