SCXML Test 350 uses datamodel-specific expression

test350.txml has this:
<data conf:id="1" conf:expr="'#_scxml_' + _sessionid”/>

This assumes that the data model uses the + operator for string concatenation. (Lua does not.)
The simplest conversion would probably be to use the existing conf:concatVars, after stuffing those two variables into the data model, as in test190.txml

For example:

<datamodel>
  <data conf:id="1" conf:quoteExpr="#_scxml_"/>
  <data conf:id="2" conf:systemVarExpr="_sessionid”/>
</datamodel>
…
<state id="s0"><onentry><conf:concatVars id1="1" id2="2"/>