Fix enum DEFAULT NULL validation in analyzer

- Add missing case for NULL values in validateEnumLiteralDefault function
- MySQL allows DEFAULT NULL for enum columns, but analyzer was rejecting it
- This fixes CREATE TABLE statements with enum columns that have DEFAULT NULL
- Resolves "incompatible type for default value" error for valid enum defaults

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: elianddb

sql/analyzer/resolve_column_defaults.go

@@ -296,6 +296,9 @@ func validateEnumLiteralDefault(enumType sql.EnumType, colDefault *sql.ColumnDef
 	}
 
 	switch v := val.(type) {
+	case nil:
+		// NULL is a valid default for enum columns
+		return nil
 	case string:
 		// For string values, check if it's a direct enum value match
 		enumValues := enumType.Values()

sql/expression/enum.go

@@ -80,7 +80,7 @@ func (e *EnumToString) Eval(ctx *sql.Context, row sql.Row) (interface{}, error)
 	case string:
 		str = v
 	default:
-		return nil, sql.ErrInvalidType.New(val, types.Text)
+		return nil, sql.ErrInvalidType.New(types.Text.String())
 	}
 	return str, nil
 }

sql/types/enum.go

@@ -165,13 +165,13 @@ func (t EnumType) Convert(ctx context.Context, v interface{}) (interface{}, sql.
 
 	switch value := v.(type) {
 	case int:
+		if _, ok := t.At(value); ok {
+			return uint16(value), sql.InRange, nil
+		}
 		// MySQL rejects 0 values in strict mode regardless of enum definition
 		if value == 0 && t.validateScrictMode(ctx) {
 			return nil, sql.OutOfRange, ErrConvertingToEnum.New(value)
 		}
-		if _, ok := t.At(value); ok {
-			return uint16(value), sql.InRange, nil
-		}
 	case uint:
 		return t.Convert(ctx, int(value))
 	case int8:
@@ -224,6 +224,7 @@ func (t EnumType) validateScrictMode(ctx context.Context) bool {
 	return false
 }
 
+
 // Equals implements the Type interface.
 func (t EnumType) Equals(otherType sql.Type) bool {
 	if ot, ok := otherType.(EnumType); ok && t.collation.Equals(ot.collation) && len(t.idxToVal) == len(ot.idxToVal) {