Comment 9 for bug 1446746

Also had this problem with after an upgrade from Xubuntu 14.10 to 15.05
(xubuntu was installed on top of ubuntu server without recommends if that helps)

Following kgoeser advice I used `sudo apt-get build-dep gitg` to generate a list of missing build dependences:

The following NEW packages will be installed:
  autopoint dh-autoreconf gir1.2-atspi-2.0 gir1.2-gconf-2.0 gir1.2-gdesktopenums-3.0 gir1.2-gee-0.8 gir1.2-git2-glib-1.0 gir1.2-gtksource-3.0 gir1.2-gtkspell3-3.0 gir1.2-javascriptcoregtk-4.0 gir1.2-json-1.0 gir1.2-peas-1.0
  gir1.2-secret-1 gir1.2-webkit2-4.0 gnome-common gobject-introspection gsettings-desktop-schemas-dev intltool libatk-bridge2.0-dev libatspi2.0-dev libenchant-dev libgconf2-dev libgcrypt20-dev libgee-0.8-dev libgirepository1.0-dev
  libgit2-dev libgit2-glib-1.0-dev libgpg-error-dev libgtk-3-dev libgtksourceview-3.0-dev libgtkspell3-3-dev libhttp-parser-dev libjavascriptcoregtk-4.0-dev libjson-glib-dev libpeas-dev libsecret-1-dev libsoup2.4-dev libssh2-1-dev
  libvala-0.26-0 libwebkit2gtk-4.0-dev libxtst-dev valac valac-0.26 valac-0.26-vapi x11proto-record-dev

I don’t like installing unnecessary stuff so I cancelled that and took a punt that I was only missing `gir1.2-peas-1.0`.

After a:

sudo apt-get install gir1.2-peas-1.0

gitg was all working without errors :)