Uninitialized strings break simulation

[n1kPLV]

This triggers the bug described in #53, however I think this a separate problem.
When a string is declared but not initialized in an scchart, but is assigned at a later point, the simulation stops with the error message described in #53

Reproduction

Consider the SCChart

scchart Un_STR {
    output string out

    input bool step

    initial state a
    if step go to b

    state b{
        entry do out = "aaa"
    }
}

Start a simulation of this scchart. If you use java based simulation, you need to set step to true. Then advance the simulation by one or two steps.

Expected behavior

The now initialized string shows up in the variable list with its new value. The simulation continues

Actual behavior

The Simulation is stopped. The error message from #53 appears in the Simulation output.