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src/Features/Core/Portable/IncrementalCaches/SymbolTreeInfoIncrementalAnalyzerProvider.cs

@@ -52,6 +52,11 @@ public ProjectInfo(VersionStamp versionStamp, SymbolTreeInfo info)
         private struct MetadataInfo
         {
             public readonly DateTime TimeStamp;
+
+            /// <summary>
+            /// Note: can be <code>null</code> if were unable to create a SymbolTreeInfo
+            /// (for example, if the metadata was bogus and we couldn't read it in).
+            /// </summary>
             public readonly SymbolTreeInfo SymbolTreeInfo;
 
             /// <summary>