Fix Invalid data in Session

[sveneld]

Motivation and Context

During the testsing of my application I got an error

/vendor/mcp/sdk/src/Server/Session/Session.php in Mcp\Server\Session\Session::readData at line 174
/vendor/mcp/sdk/src/Server/Session/Session.php in Mcp\Server\Session\Session::set at line 75
/vendor/mcp/sdk/src/Server/Protocol.php in Mcp\Server\Protocol::handleRequest at line 163
/vendor/mcp/sdk/src/Server/Protocol.php in Mcp\Server\Protocol::processInput at line 130
/vendor/mcp/sdk/src/Server/Transport/BaseTransport.php in Mcp\Server\Transport\BaseTransport::handleMessage at line 133

How Has This Been Tested?

OAuth implementation

Breaking Changes

No

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[Nyholm]

Thank you