B4J Question cannot access DataLengthException

instead of explaining :

1. start a new b4j project
2. add jB4XEncryption library
3. add the following sub :
Sub compileError(src()As Byte,pass As String) As Byte()
Dim enc As B4XCipher
Dim retVal() As Byte
Try
retVal= enc.Decrypt(src,pass)
Return retVal
Catch
''
End Try
End Sub

4. try to compile . I'm getting the error in the question header
5. exactly the same code works ok in b4a. what's the problem ?

Thank you