Nextcloud 14 and PHP 7.0 on Debian 9: empty page / segfault [solved]

Nextcloud version: 14.0.3
Operating system and version (eg, Ubuntu 17.04): Debian 9.5
Apache or nginx version (eg, Apache 2.4.25): 2.4.25-3+deb9u5
PHP version (eg, 7.1): 7.0.30-0+deb9u1

When upgrading from Nextcloud 13 to Nextcloud 14, it requires PHP 7, so I had to switch from PHP 5 to PHP 7.
Documentation is mentionning 7.0, 7.1 and 7.2 are supported.
Debian stable = Debian 9.5 (stretch) is running with PHP 7.0.30, so I installed this version using debian packages.

But after successful login on Nextcloud 14, apache2 is crashing with a segfault:

[Fri Oct 12 21:51:03.057774 2018] [core:notice] [pid 2573] AH00052: child pid 2607 exit signal Segmentation fault (11)

Strace is not helping much:
open("/dev/urandom", O_RDONLY|O_NOCTTY|O_NONBLOCK) = 38
fstat(38, {st_mode=S_IFCHR|0666, st_rdev=makedev(1, 9), …}) = 0
poll([{fd=38, events=POLLIN}], 1, 10) = 1 ([{fd=38, revents=POLLIN}])
read(38, “\201\26$~%<\22\230\364r\240\262\r\365l\315\237*\261\347>\242o\334\317v\231\265\30Xn9”, 32) = 32
close(38) = 0
getuid() = 33
— SIGSEGV {si_signo=SIGSEGV, si_code=SI_KERNEL, si_addr=NULL} —

I found a workaround to fix that issue => upgrade to PHP 7.2 (packages from Debian 10 aka buster/testing)…
If that can help some other folks…

If Nextcloud is not supporting PHP 7.0, can we update documentation to mention it? That would have saved me several hours of troubleshooting… (note that means Debian 9.5, aka stable/stretch is not supported then, NC 14 requires then Debian 10 / testing).

Why is Nextcloud not supporting php 7.0? Because of your error?