The use of switch statements inside a bounded for loop resulted in some
false positives regarding the "default:" label which cannot be reached
since each of the other case statements use the possible for loop values.
A [dead_error_begin] was added before the default label.

Commit id ebdbe25a adjusted the algorithm and the caller guarantees that
the 'params' will have a '_' in the name being searched. Add the [returned_null]
tag to the two instances.