Implement converting void type

for the SMT2 queries.

Author: petr-bauch

src/solvers/smt2/smt2_conv.cpp

@@ -2214,6 +2214,10 @@ void smt2_convt::convert_typecast(const typecast_exprt &expr)
         convert_typecast(tmp);
       }
     }
+    else if(src_type.id() == ID_empty)
+    {
+      convert_expr(src);
+    }
     else
     {
       std::ostringstream e_str;
@@ -4626,6 +4630,11 @@ void smt2_convt::convert_type(const typet &type)
   {
     convert_type(c_bit_field_replacement_type(to_c_bit_field_type(type), ns));
   }
+  else if(type.id() == ID_empty)
+  {
+    // the NONDET(void) is in fact of type char
+    out << "(_ BitVec " << boolbv_width(char_type()) << " )";
+  }
   else
   {
     UNEXPECTEDCASE("unsupported type: "+type.id_string());