As you can see in the following example (from plantuml site), `State2` can be rendered with a simple box. But right now it shows as a box with two partitions, one of which is empty. For large diagrams, this unnecessarily takes a lot of space.
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You can use "hide empty description" command :
@startuml hide empty description [*] --> State1 State1 --> [*] State1 : this is a string State1 : this is another string State1 -> State2 State2 --> [*] @enduml
http://www.plantuml.com/plantuml/uml/SoWkIImgAStDuSh8J4bLICqjAAbKI4ajJYxAB2Z9pC_ZYjQALT3LjLC8BaaiIJNaWb1W4Q0CZ6kbK9AHMQm0H8aAnIL5cNdfM6JoyaioKejWyZ05CAEDk20Kt6Y7rBmKeBi0