Strange XSD.String error
## Summary
Originally reported in the forum: https://www.eclipse.org/forums/index.php/t/1116105/
We found a strange compiler error when mixing XSD.String and charstrings in assignments.
```
function f_Test() {
var XSD.String v_Str1 := "123";
var charstring v_Str2 := "456";
var charstring v_Str3 := v_Str1 & v_Str2; // <--- ??? causes an error
var charstring v_Str4 := v_Str2 & v_Str1; // does not cause an error !
log(v_Str3);
log(v_Str4);
}
```
issue