SeriesServiceImplTest: correct test name.

Should be in 795edcc commit.

No functional changes.

[ci skip]

Author: php-coder

src/test/groovy/ru/mystamps/web/service/SeriesServiceImplTest.groovy

@@ -79,7 +79,7 @@ class SeriesServiceImplTest extends Specification {
 	// Tests for add()
 	//
 
-	def "add() should throw exception argument is null"() {
+	def "add() should throw exception if dto is null"() {
 		when:
 			service.add(null, userId, false)
 		then: