[rc2] Fix null reference exception in migrations when string has invalid store type

src/EFCore.Relational/Migrations/MigrationsSqlGenerator.cs

@@ -1356,7 +1356,8 @@ protected virtual void ColumnDefinition(
             return;
         }
 
-        var columnType = operation.ColumnType ?? GetColumnType(schema, table, name, operation, model)!;
+        var columnType = operation.ColumnType ?? GetColumnType(schema, table, name, operation, model);
+
         builder
             .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(name))
             .Append(" ")
@@ -1401,7 +1402,7 @@ protected virtual void ComputedColumnDefinition(
     /// <param name="operation">The column metadata.</param>
     /// <param name="model">The target model which may be <see langword="null" /> if the operations exist without a model.</param>
     /// <returns>The database/store type for the column.</returns>
-    protected virtual string? GetColumnType(
+    protected virtual string GetColumnType(
         string? schema,
         string tableName,
         string name,
@@ -1429,7 +1430,7 @@ protected virtual void ComputedColumnDefinition(
                 || table.Indexes.Any(u => u.Columns.Contains(column));
         }
 
-        return Dependencies.TypeMappingSource.FindMapping(
+        var storeType = Dependencies.TypeMappingSource.FindMapping(
                 operation.ClrType,
                 null,
                 keyOrIndex,
@@ -1440,6 +1441,15 @@ protected virtual void ComputedColumnDefinition(
                 operation.Precision,
                 operation.Scale)
             ?.StoreType;
+
+        if (storeType != null)
+        {
+            return storeType;
+        }
+
+        var fullTableName = schema != null ? $"{schema}.{tableName}" : tableName;
+        throw new InvalidOperationException(
+            RelationalStrings.UnsupportedTypeForColumn(fullTableName, name, operation.ClrType?.Name ?? "unknown"));
     }
 
     /// <summary>

src/EFCore.Relational/Properties/RelationalStrings.resx

@@ -1306,6 +1306,9 @@
   <data name="UnsupportedType" xml:space="preserve">
     <value>The current provider doesn't have a store type mapping for properties of type '{clrType}'.</value>
   </data>
+  <data name="UnsupportedTypeForColumn" xml:space="preserve">
+    <value>Unable to find a store type mapping for column '{table}.{column}' with CLR type '{clrType}'.</value>
+  </data>
   <data name="UpdateConcurrencyException" xml:space="preserve">
     <value>The database operation was expected to affect {expectedRows} row(s), but actually affected {actualRows} row(s); data may have been modified or deleted since entities were loaded. See https://go.microsoft.com/fwlink/?LinkId=527962 for information on understanding and handling optimistic concurrency exceptions.</value>
   </data>

src/EFCore.SqlServer/Migrations/SqlServerMigrationsSqlGenerator.cs

@@ -383,9 +383,7 @@ protected override void Generate(
             {
                 Check.DebugAssert(operation.DefaultValue is not null);
 
-                var typeMapping = (columnType != null
-                        ? Dependencies.TypeMappingSource.FindMapping(operation.DefaultValue.GetType(), columnType)
-                        : null)
+                var typeMapping = Dependencies.TypeMappingSource.FindMapping(operation.DefaultValue.GetType(), columnType)
                     ?? Dependencies.TypeMappingSource.GetMappingForValue(operation.DefaultValue);
 
                 defaultValueSql = typeMapping.GenerateSqlLiteral(operation.DefaultValue);
@@ -1640,7 +1638,7 @@ protected override void ColumnDefinition(
             return;
         }
 
-        var columnType = operation.ColumnType ?? GetColumnType(schema, table, name, operation, model)!;
+        var columnType = operation.ColumnType ?? GetColumnType(schema, table, name, operation, model);
         builder
             .Append(Dependencies.SqlGenerationHelper.DelimitIdentifier(name))
             .Append(" ")

src/EFCore.Sqlite.Core/Migrations/SqliteMigrationsSqlGenerator.cs

@@ -58,7 +58,7 @@ private bool IsSpatialiteColumn(AddColumnOperation operation, IModel? model)
                 operation.Table,
                 operation.Name,
                 operation,
-                model)!);
+                model));
 
     private IReadOnlyList<MigrationOperation> RewriteOperations(
         IReadOnlyList<MigrationOperation> migrationOperations,

test/EFCore.SqlServer.FunctionalTests/Migrations/SqlServerMigrationsSqlGeneratorTest.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using Microsoft.EntityFrameworkCore.Diagnostics;
 using Microsoft.EntityFrameworkCore.Metadata.Internal;
 using Microsoft.EntityFrameworkCore.SqlServer.Internal;
 using Microsoft.EntityFrameworkCore.SqlServer.Metadata.Internal;
@@ -1267,6 +1268,25 @@ FROM [sys].[default_constraints] [d]
 """);
     }
 
+
+
+    [ConditionalFact]
+    public void Invalid_column_type_for_unmappable_clr_type_throws_meaningful_exception()
+    {
+        var ex = Assert.Throws<InvalidOperationException>(() =>
+            Generate(
+                new AddColumnOperation
+                {
+                    Name = "TestColumn",
+                    Table = "TestTable",
+                    ClrType = typeof(System.IO.FileStream), // Unmappable CLR type
+                    ColumnType = null,
+                    IsNullable = false
+                }));
+
+        Assert.Equal(RelationalStrings.UnsupportedTypeForColumn("TestTable", "TestColumn", "FileStream"), ex.Message);
+    }
+
     private static void CreateGotModel(ModelBuilder b)
         => b.HasDefaultSchema("dbo").Entity(
             "Person", pb =>