Show avg block heath in pool ranking pie chart

backend/src/api/mining/mining.ts

@@ -100,7 +100,7 @@ class Mining {
         rank: rank++,
         emptyBlocks: emptyBlocksCount.length > 0 ? emptyBlocksCount[0]['count'] : 0,
         slug: poolInfo.slug,
-        avgMatchRate: Math.round(100 * poolInfo.avgMatchRate) / 100,
+        avgMatchRate: poolInfo.avgMatchRate !== null ? Math.round(100 * poolInfo.avgMatchRate) / 100 : null,
       };
       poolsStats.push(poolStat);
     });

backend/src/mempool.interfaces.ts

@@ -16,7 +16,7 @@ export interface PoolInfo {
   link: string;
   blockCount: number;
   slug: string;
-  avgMatchRate: number;
+  avgMatchRate: number | null;
 }
 
 export interface PoolStats extends PoolInfo {