Allow default value "null" for DbType.String but not for others

Author: JaBistDuNarrisch

src/Migrator.Tests/Providers/Base/TransformationProviderBase.cs

@@ -64,10 +64,9 @@ protected void DropTestTables()
         }
     }
 
-
     protected async Task BeginOracleTransactionAsync()
     {
-        using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10));
+        using var cts = new CancellationTokenSource(TimeSpan.FromMinutes(1));
         var configReader = new ConfigurationReader();
 
         var databaseConnectionConfig = configReader.GetDatabaseConnectionConfigById(DatabaseConnectionConfigIds.OracleId);

src/Migrator/Providers/Impl/Oracle/OracleTransformationProvider.cs

@@ -635,7 +635,11 @@ public override Column[] GetColumns(string table)
                 }
 
                 // dataDefaultString contains ISEQ$$ if the column is an identity column
-                if (!string.IsNullOrWhiteSpace(dataDefaultString) && !dataDefaultString.Equals("null", StringComparison.OrdinalIgnoreCase) && !dataDefaultString.Contains("ISEQ$$") && !dataDefaultString.Contains(".nextval"))
+                if (
+                    !string.IsNullOrWhiteSpace(dataDefaultString) &&
+                    (column.Type == DbType.String || !dataDefaultString.Equals("null", StringComparison.OrdinalIgnoreCase)) &&
+                    !dataDefaultString.Contains("ISEQ$$") &&
+                    !dataDefaultString.Contains(".nextval"))
                 {
                     // This is only necessary because older versions of this migrator added single quotes for numerics.
                     var singleQuoteStrippedString = dataDefaultString.Replace("'", "");