Add some more tests for RID related types

Author: ericstj

src/Microsoft.DotNet.Build.Tasks.Packaging/src/GenerateRuntimeGraph.cs

@@ -309,6 +309,12 @@ private void AddInferredRuntimeIdentifiers(ICollection<RuntimeGroup> runtimeGrou
                             continue;
                         }
 
+                        if (!rid.HasVersion())
+                        {
+                            closestGroup = candidate;
+                            continue;
+                        }
+
                         foreach(var version in candidate.Versions)
                         {
                             if (closestVersion == null || 
@@ -344,7 +350,7 @@ private void AddInferredRuntimeIdentifiers(ICollection<RuntimeGroup> runtimeGrou
                         candidateRuntimeGroups.Add(runtimeGroup);
 
                     }
-                    else if (closestVersion != rid.Version)
+                    else if (rid.HasVersion() && closestVersion != rid.Version)
                     {
                         closestGroup.Versions.Add(rid.Version);
                     }

src/Microsoft.DotNet.Build.Tasks.Packaging/src/RuntimeVersion.cs

@@ -50,7 +50,12 @@ public int CompareTo(object obj)
 
         public int CompareTo(RuntimeVersion other)
         {
-            int versionResult = version.CompareTo(other.version);
+            if (other == null)
+            {
+                return 1;
+            }
+
+            int versionResult = version.CompareTo(other?.version);
 
             if (versionResult == 0)
             {
@@ -73,7 +78,8 @@ public int CompareTo(RuntimeVersion other)
         public bool Equals(RuntimeVersion other)
         {
             return object.ReferenceEquals(other, this) ||
-                versionString.Equals(other.versionString, StringComparison.Ordinal);
+                (other != null && 
+                versionString.Equals(other.versionString, StringComparison.Ordinal));
         }
 
         public override bool Equals(object obj)