Merge pull request #1092 from NilPuig/fix/memory-usage-nil-guard

Fix nil panic in memoryUsageCmd Lua script

internal/rdb/inspect.go

@@ -264,8 +264,10 @@ for i=1,2 do
     if (table.getn(ids) > 0) then
         for _, id in ipairs(ids) do
             local bytes = redis.call("MEMORY", "USAGE", ARGV[1] .. id)
+            if bytes then
                 sample_total = sample_total + bytes
             end
+        end
         local n = redis.call("LLEN", KEYS[i])
         local avg = sample_total / table.getn(ids)
         memusg = memusg + (avg * n)
@@ -281,8 +283,10 @@ for i=3,6 do
     if (table.getn(ids) > 0) then
         for _, id in ipairs(ids) do
             local bytes = redis.call("MEMORY", "USAGE", ARGV[1] .. id)
+            if bytes then
                 sample_total = sample_total + bytes
             end
+        end
         local n = redis.call("ZCARD", KEYS[i])
         local avg = sample_total / table.getn(ids)
         memusg = memusg + (avg * n)
@@ -304,14 +308,18 @@ if table.getn(groups) > 0 then
 			local ids = redis.call("ZRANGE", group_key, 0, sample_size - 1)
 			for _, id in ipairs(ids) do
 				local bytes = redis.call("MEMORY", "USAGE", ARGV[1] .. id)
+				if bytes then
 					agg_task_sample_total = agg_task_sample_total + bytes
 					agg_task_sample_size = agg_task_sample_size + 1
 				end
 			end
 		end
+	end
+	if agg_task_sample_size > 0 then
 		local avg = agg_task_sample_total / agg_task_sample_size
 		memusg = memusg + (avg * agg_task_count)
 	end
+end
 return memusg
 `)