dotnet/releases/net472/KnownIssues/611802 - SQLConnection.Conn...

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# NullReferenceException while setting `SqlConnection.ConnectionString` to an empty string or null.
## Symptoms
When an application tries to set the `ConnectionString` property of the `SqlConnection` object to an empty string or null value, a `NullReferenceException` is thrown. This exception occurs when .NET Framework 4.7.2 is installed on the OS hosting the application.
## Cause
.NET Framework 4.7.2 includes a change that increases the default connection retry count for connections to Azure SQL Database to two.
This change sets the internal value of the retry count without validating if the `ConnectionString` is a non-null or non-empty value,
which results in the `NullReferenceException`.
## Impact
The impact is limited to applications using the `SqlConnection.ConnectionString` API to set an empty connection string, which now throws an exception.
## Workarounds
No known workarounds with .NET Framework 4.7.2.
## Resolution
This issue has been fixed in the [latest update to .NET Framework 4.7.2](https://go.microsoft.com/fwlink/?LinkId=2005309) for all platforms except Windows 10 April 2018 Update.
For Windows 10 April 2018 Update, the fix will be available in the upcoming Cumulative Update.