Use of uninitized prev variable
The CI job #52072 failed showing a merge output with the first item skipped.
This failure is caused by the use of uninitialized memory
prev_b due to the input array
a being empty. This only occurs with the
DROP_IN_INPUT duplicate strategy. The same issue can occur if
prev is uninitialized due to an empty input array
a with the duplicate strategy
DROP. In both cases the
prev_b value has the same value as the first item in array
b and is thus skipped.