populate_sdk_ext: do not require CONF_VERSION (e.g. local.conf version) to be set

The version checks for local.conf/site.conf/bblayers.conf are all optional,
and aren't enforced (by insane class) if the versions aren't set.

As bitbake-setup writes out a blank local.conf, it doesn't put a version in it
either. Also, esdk bundle has a fixed set of layers and is not at risk of
needing to update its own local.conf.

The same condition is already in place for esdk's bblayers.conf for similar reasons.

(From OE-Core rev: d83ff28157aaa9322f98b8da5dd50b562085085a)

Signed-off-by: Alexander Kanavin <alex@linutronix.de>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/classes-recipe/populate_sdk_ext.bbclass

@@ -345,7 +345,13 @@ def write_local_conf(d, baseoutpath, derivative, core_meta_subdir, uninative_che
             if bb.data.inherits_class('uninative', d):
                f.write('INHERIT += "%s"\n' % 'uninative')
                f.write('UNINATIVE_CHECKSUM[%s] = "%s"\n\n' % (d.getVar('BUILD_ARCH'), uninative_checksum))
-            f.write('CONF_VERSION = "%s"\n\n' % d.getVar('CONF_VERSION', False))
+
+            # CONF_VERSION may not be set, for example when using an empty local.conf
+            # generated with bitbake-setup, and it is not otherwise required to exist.
+            # Write it out only if it's defined.
+            conf_version = d.getVar('CONF_VERSION', False)
+            if conf_version is not None:
+                f.write('CONF_VERSION = "%s"\n\n' % conf_version)
 
             # Some classes are not suitable for SDK, remove them from INHERIT
             f.write('INHERIT:remove = "%s"\n' % d.getVar('ESDK_CLASS_INHERIT_DISABLE', False))