Fix NullReferenceException in CommandBatchPreparer.FormatValues hiding circular dependency errors

[Copilot]

When Entity Framework Core encounters circular dependencies during SaveChanges(), it attempts to generate a helpful error message that includes details about the entities involved. However, when sensitive data logging is enabled, a NullReferenceException can occur in the CommandBatchPreparer.FormatValues method, which hides the actual circular dependency error from users.

The issue occurs because the FormatValues method assumes the values parameter is never null, but in certain edge cases (particularly with circular dependencies), the value factory methods (CreateDependentKeyValue, CreateKeyValue, CreateIndexValue) can return null. When this happens, accessing values[i] throws a NullReferenceException that masks the real error.

Example of the problem:

Before this fix, users would see:

Object reference not set to an instance of an object.
   at Microsoft.EntityFrameworkCore.Update.Internal.CommandBatchPreparer.FormatValues(Object[] values, IReadOnlyList1 columns, IReadOnlyModificationCommand dependentCommand, StringBuilder builder)

After this fix, users will see the actual error:

System.InvalidOperationException: Unable to save changes because a circular dependency was detected in the data to be saved: 'Entity [Added] ForeignKeyConstraint { 'ForeignKey' } <- RelatedEntity [Modified] <- Index { 'UniqueColumn' } Entity [Added]To show additional information call 'DbContextOptionsBuilder.EnableSensitiveDataLogging'.'.

Solution:

Added a null check for the values parameter in the FormatValues method. When values is null, the method now outputs "NULL" for each column instead of attempting to access the array, allowing the real circular dependency error to be properly displayed to users.

The fix is minimal and surgical - it only adds a null check without changing any existing behavior when values is non-null.

Fixes #35665.

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[roji]

@AndriySvyryd any idea how this didn't trigger an NRT warning/error?

[AndriySvyryd]

@AndriySvyryd any idea how this didn't trigger an NRT warning/error?

Because it was suppressed 🤦