Better handling of VersionId being missing.

Author: GurliGebis

src/managed/Microsoft.DotNet.PlatformAbstractions/Native/PlatformApis.cs

@@ -128,14 +128,8 @@ private static DistroInfo LoadDistroInfo()
         // are backwards compatible.
         private static DistroInfo NormalizeDistroInfo(DistroInfo distroInfo)
         {
-            if (string.IsNullOrEmpty(distroInfo.VersionId))
-            {
-                // Some distribution does not have VERSION_ID defined.
-                // Since we need it, we workaround this by giving it the value "unavailable".
-                distroInfo.VersionId = "unavailable";
-            }
-
-            int minorVersionNumberSeparatorIndex = distroInfo.VersionId.IndexOf('.');
+            // Handle if VersionId is null by just setting the index to -1.
+            int minorVersionNumberSeparatorIndex = distroInfo.VersionId?.IndexOf('.') ?? -1;
 
             if (distroInfo.Id == "rhel" && minorVersionNumberSeparatorIndex != -1)
             {

src/managed/Microsoft.DotNet.PlatformAbstractions/RuntimeEnvironment.cs

@@ -52,6 +52,11 @@ private static string GetRIDVersion()
                 case Platform.Windows:
                     return GetWindowsProductVersion();
                 case Platform.Linux:
+                    if (string.IsNullOrEmpty(OperatingSystemVersion))
+                    {
+                        return string.Empty;
+                    }
+
                     return $".{OperatingSystemVersion}";
                 case Platform.Darwin:
                     return $".{OperatingSystemVersion}";