  GRB 111005A, one long duration gamma-ray burst (GRB) occurred within a
metal-rich environment that lacks massive stars with $M_{\rm ZAMS}\geq
15M_\odot$, is not coincident with supernova emission down to stringent limit
and thus should be classified as a "long-short" GRB (lsGRB; also known as
SN-less long GRB or hybrid GRB), like GRB 060505 and GRB 060614. In this work
we show that in the neutron star merger model, the non-detection of the
optical/infrared emission of GRB 111005A requires a sub-relativistic
neutron-rich ejecta with the mass of $\leq 0.01~M_\odot$, (significantly) less
massive than that of GRB 130603B, GRB 060614 and GRB 050709. The lsGRBs are
found to have a high rate density and the neutron star merger origin model can
be unambiguously tested by the joint observations of the second generation
gravitational wave (GW) detectors and the full-sky gamma-ray monitors such as
Fermi-GBM and the proposing GECAM. If no lsGRB/GW association is observed in
2020s, alternative scenarios have to be systematically investigated. With the
detailed environmental information achievable for the very-nearby events, a
novel kind of merger or explosion origin may be identified.
