Fix tests and add missing null checks...

src/EditorFeatures/Core/Implementation/Workspaces/ProjectCacheService.SimpleMRUCache.cs

@@ -18,7 +18,7 @@ private class SimpleMRUCache
 
             private readonly Node[] _nodes = new Node[CacheSize];
 
-            public bool Empty
+            public bool IsEmpty
             {
                 get
                 {

src/EditorFeatures/Core/Implementation/Workspaces/ProjectCacheService.cs

@@ -39,7 +39,7 @@ public bool IsImplicitCacheEmpty
             {
                 lock (_gate)
                 {
-                    return _implicitCache.Empty;
+                    return _implicitCache?.IsEmpty ?? false;
                 }
             }
         }
@@ -48,7 +48,7 @@ public void ClearImplicitCache()
         {
             lock (_gate)
             {
-                _implicitCache.Clear();
+                _implicitCache?.Clear();
             }
         }
 
@@ -56,7 +56,7 @@ public void ClearExpiredImplicitCache(DateTime expirationTime)
         {
             lock (_gate)
             {
-                _implicitCache.ClearExpiredItems(expirationTime);
+                _implicitCache?.ClearExpiredItems(expirationTime);
             }
         }
 

src/EditorFeatures/Test/Workspaces/ProjectCacheHostServiceFactoryTests.cs

@@ -107,7 +107,8 @@ public void TestCacheDoesNotKeepObjectsAliveAfterOwnerIsCollected2()
         [Fact]
         public void TestImplicitCacheKeepsObjectAlive1()
         {
-            var cacheService = new ProjectCacheService(null, int.MaxValue);
+            var workspace = new AdhocWorkspace(MockHostServices.Instance, workspaceKind: WorkspaceKind.Host);
+            var cacheService = new ProjectCacheService(workspace, int.MaxValue);
             var instance = new object();
             var weak = new WeakReference(instance);
             cacheService.CacheObjectIfCachingEnabledForKey(ProjectId.CreateNewId(), (object)null, instance);
@@ -201,7 +202,8 @@ public void TestEjectFromImplicitCache()
             var weakFirst = new WeakReference(compilations[0]);
             var weakLast = new WeakReference(compilations[compilations.Count - 1]);
 
-            var cache = new ProjectCacheService(null, int.MaxValue);
+            var workspace = new AdhocWorkspace(MockHostServices.Instance, workspaceKind: WorkspaceKind.Host);
+            var cache = new ProjectCacheService(workspace, int.MaxValue);
             for (int i = 0; i < ProjectCacheService.ImplicitCacheSize + 1; i++)
             {
                 cache.CacheObjectIfCachingEnabledForKey(ProjectId.CreateNewId(), (object)null, compilations[i]);
@@ -225,7 +227,8 @@ public void TestCacheCompilationTwice()
             var weak3 = new WeakReference(comp3);
             var weak1 = new WeakReference(comp1);
 
-            var cache = new ProjectCacheService(null, int.MaxValue);
+            var workspace = new AdhocWorkspace(MockHostServices.Instance, workspaceKind: WorkspaceKind.Host);
+            var cache = new ProjectCacheService(workspace, int.MaxValue);
             var key = ProjectId.CreateNewId();
             var owner = new object();
             cache.CacheObjectIfCachingEnabledForKey(key, owner, comp1);