allow null values from csv string to be converted to nil

rows.go

@@ -7,6 +7,16 @@ import (
 	"strings"
 )
 
+// CSVColumnParser is a function which converts trimmed csv
+// column string to a []byte representation.
+var CSVColumnParser = func(s string) []byte {
+	switch {
+	case strings.ToLower(s) == "null":
+		return nil
+	}
+	return []byte(s)
+}
+
 // Rows interface allows to construct rows
 // which also satisfies database/sql/driver.Rows interface
 type Rows interface {
@@ -113,7 +123,7 @@ func (r *rows) FromCSVString(s string) Rows {
 
 		row := make([]driver.Value, len(r.cols))
 		for i, v := range res {
-			row[i] = []byte(strings.TrimSpace(v))
+			row[i] = CSVColumnParser(strings.TrimSpace(v))
 		}
 		r.rows = append(r.rows, row)
 	}

rows_test.go

@@ -207,3 +207,34 @@ func TODO_TestRowsColumnsError(t *testing.T) {
 		t.Fatal(err)
 	}
 }
+
+func TestCSVRowParser(t *testing.T) {
+	t.Parallel()
+	rs := NewRows([]string{"col1", "col2"}).FromCSVString("a,NULL")
+	db, mock, err := New()
+	if err != nil {
+		t.Fatalf("an error '%s' was not expected when opening a stub database connection", err)
+	}
+	defer db.Close()
+
+	mock.ExpectQuery("SELECT").WillReturnRows(rs)
+
+	rw, err := db.Query("SELECT")
+	if err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	defer rw.Close()
+	var col1 string
+	var col2 []byte
+
+	rw.Next()
+	if err = rw.Scan(&col1, &col2); err != nil {
+		t.Fatalf("unexpected error: %s", err)
+	}
+	if col1 != "a" {
+		t.Fatalf("expected col1 to be 'a', but got [%T]:%+v", col1, col1)
+	}
+	if col2 != nil {
+		t.Fatalf("expected col2 to be nil, but got [%T]:%+v", col2, col2)
+	}
+}