[BUG] parseXER drops relationships whose lag_hr_cnt is blank (P6 6.0 exports write zero lag as empty) #17

Engine: v2.10.14 (also seen on v2.10.13)

What happens: Some older P6 exports (ERMHDR 6.0) write a zero lag as an empty lag_hr_cnt instead of 0. parseXER treats the empty value as non-finite and drops the relationship (ALERT lag-non-finite). In one
2,880-activity export, 2,614 of 3,235 relationships were dropped and the project finish came out 19 days earlier than P6's.

Evidence that P6 reads blank as 0: in that file, P6's own stored early dates satisfy every relationship with lag = 0 (0 forward-pass violations;
2,878 of 2,880 early starts tight to their driving predecessor, the other 2 set by constraints). With the blank lags set to 0, the engine matched P6's stored values on all 2,880 activities: ES, EF, LS, LF to the minute, TF and FF (< 0.01 h) and the critical flag.

Minimal reproduction (attached, synthetic): two activities, A (40 h)
-> B (24 h), FS with an empty lag_hr_cnt.

• lag_hr_cnt = "" -> 0 relationships kept, B early start 2026-01-05, finish 2026-01-12, ALERT lag-non-finite
• lag_hr_cnt = "0" -> 1 relationship kept, B early start 2026-01-12, finish 2026-01-15

Suggestion: treat an empty lag_hr_cnt as 0 (with an INFO note for traceability) and keep the ALERT for genuinely malformed values (NaN, text).

The original export is not mine to share, but I'm happy to re-test a fix against it.