Java Back-end Incompatible Types: Bad Return type in Lambda Expression

```dafny
datatype D = A | B

method Main() {
    print match A {
        case A => 'c'
        case _ => 'a'
    };
}
```
throws the following exception when compiling to Java: 
```code
error: incompatible types: bad return type in lambda expression
```
(will fill rest in later)