sql: Support nil values

sql.go

@@ -14,6 +14,9 @@ import (
 // consult database-specific driver documentation for matching types.
 func (uuid *UUID) Scan(src interface{}) error {
 	switch src := src.(type) {
+	case nil:
+		return nil
+
 	case string:
 		// if an empty UUID comes from a table, we return a null UUID
 		if src == "" {

sql_test.go

@@ -90,6 +90,17 @@ func TestScan(t *testing.T) {
 			t.Error("UUID was not nil after scanning empty byte slice")
 		}
 	}
+
+	uuid = UUID{}
+	err = (&uuid).Scan(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, v := range uuid {
+		if v != 0 {
+			t.Error("UUID was not nil after scanning nil")
+		}
+	}
 }
 
 func TestValue(t *testing.T) {