Fix NullReferenceExceptions in expressions and connection strings

[pumpkin-bit]

Problem/Bug

Following an audit of the System.Data.Common library's code, comments marked “TODO: Possible bug” were discovered, indicating unhandled edge cases specifically working with empty or null values in expressions could result in exceptions NullReferenceException and ArgumentNullException.

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Solution

DataTable.cs: A check for dc.DataExpression != null has been added to the EvaluateDependentExpressions method. This prevents a NullReferenceException from occurring if the column expression has been deleted or cleared.

DataExpression.cs: Fixed a conversion error in the Evaluate method we now check that _dataType != null before passing data to SqlConvert.ChangeType2 which prevents an ArgumentNullException from being thrown when evaluating untyped expressions

DbConnectionOptions.Common.cs: Fixed parsing of connection strings previously, an empty value for a Boolean flag caused a NullReferenceException due to a call to .Trim() on a null string this case is now safely handled and throws a standard ArgumentException

Fixed:

TODO: Possible bug: dc.DataExpression may be null
TODO: _dataType can be null this is likely a bug
TODO: Is it possible for _parsetable to contain a null value here? If so there's a bug here, investigate.

Testing

I've also attached tests to this PR

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[Copilot]

Pull request overview

This PR addresses reported NullReferenceException / ArgumentNullException edge cases in System.Data.Common by hardening expression evaluation and connection-string boolean parsing when internal state contains null values.

Changes:

• DataTable.EvaluateDependentExpressions: skip evaluation for dependent columns whose DataExpression is null.
• DataExpression.Evaluate: avoid calling SqlConvert.ChangeType2 when _dataType is null (and use a safe format provider when _table is null).
• DbConnectionOptions: treat null boolean option values as invalid and throw ArgumentException (via existing ADP.InvalidConnectionOptionValue) rather than throwing NullReferenceException.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/libraries/System.Data.Common/tests/System/Data/DataTableTest.cs	Adds regression tests for null expressions / null _dataType scenarios (currently contains reflection issues that can break/skip coverage).
src/libraries/System.Data.Common/tests/System/Data/Common/DbConnectionStringBuilderTest.cs	Adds a regression test for empty boolean option values (currently can silently pass without executing).
src/libraries/System.Data.Common/src/System/Data/Filter/DataExpression.cs	Avoids ChangeType2 when _dataType is null and uses a safe format provider when _table is null.
src/libraries/System.Data.Common/src/System/Data/DataTable.cs	Avoids NRE by skipping dependent-expression evaluation when dc.DataExpression is null.
src/libraries/Common/src/System/Data/Common/DbConnectionOptions.Common.cs	Allows null values through boolean conversion logic and throws standard invalid-option exceptions instead of NRE.