Prevent crash when non-advertised Class omits Context. Fixes #5651.

1 files changed, 18 insertions, 15 deletions

diff --git a/src/WixToolset.Core/Compiler.cs b/src/WixToolset.Core/Compiler.cs
index 437c1481..a4c289f7 100644
--- a/src/WixToolset.Core/Compiler.cs
+++ b/src/WixToolset.Core/Compiler.cs
@@ -1097,24 +1097,27 @@ namespace WixToolset.Core
             }
 
             HashSet<string> uniqueContexts = new HashSet<string>();
-            foreach (string context in contexts)
+            if (contexts != null)
             {
-                if (uniqueContexts.Contains(context))
-                {
-                    this.Core.Write(ErrorMessages.DuplicateContextValue(sourceLineNumbers, context));
-                }
-                else
+                foreach (string context in contexts)
                 {
-                    uniqueContexts.Add(context);
-                }
+                    if (uniqueContexts.Contains(context))
+                    {
+                        this.Core.Write(ErrorMessages.DuplicateContextValue(sourceLineNumbers, context));
+                    }
+                    else
+                    {
+                        uniqueContexts.Add(context);
+                    }
 
-                if (context.EndsWith("32", StringComparison.Ordinal))
-                {
-                    class32bit = true;
-                }
-                else
-                {
-                    class16bit = true;
+                    if (context.EndsWith("32", StringComparison.Ordinal))
+                    {
+                        class32bit = true;
+                    }
+                    else
+                    {
+                        class16bit = true;
+                    }
                 }
             }