can't install redmine [16.04]

[alper061]

dpkg sayd: Could not find gem 'mysql2 (~> 0.4.0)' in any of the gem sources listed in your Gemfile or available on this machine.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: redmine 3.2.1-1
ProcVersionSignature: Ubuntu 4.4.0-16.32-generic 4.4.6
Uname: Linux 4.4.0-16-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
ApportVersion: 2.20.1-0ubuntu1
Architecture: amd64
Date: Sun Apr 3 16:00:06 2016
InstallationDate: Installed on 2016-02-03 (60 days ago)
InstallationMedia:

PackageArchitecture: all
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: redmine
UpgradeStatus: Upgraded to xenial on 2016-04-03 (0 days ago)

[Beat Schnyder (schnyder)]

sudo apt-get install ruby-mysql2 solved the installation problem (workaround)

[Pascal A. (pascalav)]

When installing redmine through 'apt-get install redmine', you get suggested either of the SQLlite or MySQL DBMS within the installed UI. If you choose MySQL, you hit this issue indeed.

But if you install with 'apt-get install redmine redmine-mysql', you do not hit the issue.
Indeed, 'ruby-mysql' is a child/dependency of 'redmine-mysql'.