Hotfix 8706

add empty pointer check block_cache

requested review from @roman.khlopkov

assigned to @roman.khlopkov

added 5 commits

• 548e1cff...73a7df80 - 4 commits from branch release-5.2
• 07f2a923 - Merge branch 'release-5.2' of https://gitlab.demlabs.net/cellframe/cellframe-sdk into hotfix-8706

Compare with previous version

mentioned in commit b055538d

merged