Compiler [Typechecker]: Fixed reference handling in store_marker() In cases where the value passed to store_marker() was NULL but the marker was present in the mapping, we used to overwrite the marker with itself. By doing so, assign_svalue() (as used by low_mapping_insert()) would free the same value we were inserting. This is never great but has especially noticeable consequences when the value only had a single reference. Instead, we now simply do not re-insert the value in these cases.