Add support for NULL values

CONTRIBUTORS

@@ -10,3 +10,4 @@ Alexander Menzhinsky <amenzhinsky@gmail.com>
 David Skinner <skinner.david@gmail.com>
 Jan Mercl <0xjnml@gmail.com>
 Steffen Butzer <steffen(dot)butzer@outlook.com>
+Yaacov Akiba Slama <ya@slamail.org>

null_test.go

@@ -0,0 +1,26 @@
+package sqlite
+
+import (
+	"database/sql"
+	"testing"
+)
+
+func TestNullBinding(t *testing.T) {
+	db, err := sql.Open("sqlite", "file::memory:")
+	if err != nil {
+		t.Errorf("cannot open: %v", err)
+		return
+	}
+	_, err = db.Exec(`
+	CREATE TABLE table1 (field1 varchar NULL);
+	INSERT INTO table1 (field1) VALUES (?);
+	`, sql.NullString{})
+	if err != nil {
+		t.Errorf("Error binding null: %v", err)
+	}
+	err = db.Close()
+	if err != nil {
+		t.Errorf("cannot close: %v", err)
+		return
+	}
+}

sqlite.go

@@ -916,6 +916,10 @@ func (c *conn) bind(pstmt uintptr, n int, args []driver.NamedValue) (allocs []ui
 			if p, err = c.bindText(pstmt, i, x.String()); err != nil {
 				return allocs, err
 			}
+		case nil:
+			if p, err = c.bindNull(pstmt, i); err != nil {
+				return allocs, err
+			}
 		default:
 			return allocs, fmt.Errorf("sqlite: invalid driver.Value type %T", x)
 		}
@@ -926,6 +930,15 @@ func (c *conn) bind(pstmt uintptr, n int, args []driver.NamedValue) (allocs []ui
 	return allocs, nil
 }
 
+// int sqlite3_bind_null(sqlite3_stmt*, int);
+func (c *conn) bindNull(pstmt uintptr, idx1 int) (uintptr, error) {
+	if rc := sqlite3.Xsqlite3_bind_null(c.tls, pstmt, int32(idx1)); rc != sqlite3.SQLITE_OK {
+		return 0, c.errstr(rc)
+	}
+
+	return 0, nil
+}
+
 // int sqlite3_bind_text(sqlite3_stmt*,int,const char*,int,void(*)(void*));
 func (c *conn) bindText(pstmt uintptr, idx1 int, value string) (uintptr, error) {
 	p, err := libc.CString(value)