Fix sqlScannerWrapper NULL handling

https://github.com/jackc/pgx/issues/1312

pgtype/pgtype.go

@@ -1921,13 +1921,15 @@ func (w *sqlScannerWrapper) Scan(src any) error {
 	}
 
 	var bufSrc []byte
-	switch src := src.(type) {
-	case string:
-		bufSrc = []byte(src)
-	case []byte:
-		bufSrc = src
-	default:
-		bufSrc = []byte(fmt.Sprint(bufSrc))
+	if src != nil {
+		switch src := src.(type) {
+		case string:
+			bufSrc = []byte(src)
+		case []byte:
+			bufSrc = src
+		default:
+			bufSrc = []byte(fmt.Sprint(bufSrc))
+		}
 	}
 
 	return w.m.Scan(t.OID, TextFormatCode, bufSrc, w.v)

stdlib/sql_test.go

@@ -394,6 +394,10 @@ func TestConnQueryScanArray(t *testing.T) {
 		err := db.QueryRow("select '{1,2,3}'::bigint[]").Scan(m.SQLScanner(&a))
 		require.NoError(t, err)
 		assert.Equal(t, pgtype.Array[int64]{Elements: []int64{1, 2, 3}, Dims: []pgtype.ArrayDimension{{Length: 3, LowerBound: 1}}, Valid: true}, a)
+
+		err = db.QueryRow("select null::bigint[]").Scan(m.SQLScanner(&a))
+		require.NoError(t, err)
+		assert.Equal(t, pgtype.Array[int64]{Elements: nil, Dims: nil, Valid: false}, a)
 	})
 }