bitbake.conf: define empty EXTRA_IMAGE_FEATURES before using them

* fixes build without EXTRA_IMAGE_FEATURES defined:
  ERROR: '${EXTRA_IMAGE_FEATURES}' in IMAGE_FEATURES is not a valid
  image feature. Valid features: dbg-pkgs ....

(From OE-Core rev: b2cc92595b30d96a79f33ea7a7217834c8b6bff7)

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/meta/conf/bitbake.conf b/meta/conf/bitbake.conf
index fda7bc816e..174236d2fe 100644
--- a/meta/conf/bitbake.conf
+++ b/meta/conf/bitbake.conf
@@ -728,6 +728,8 @@ MACHINE_EXTRA_RDEPENDS ?= ""
 MACHINE_EXTRA_RRECOMMENDS ?= ""
 MACHINE_ESSENTIAL_EXTRA_RDEPENDS ?= ""
 MACHINE_ESSENTIAL_EXTRA_RRECOMMENDS ?= ""
+
+EXTRA_IMAGE_FEATURES ??= ""
 IMAGE_FEATURES += "${EXTRA_IMAGE_FEATURES}"
 
 DISTRO_FEATURES_BACKFILL = "pulseaudio sysvinit"