skip cache update if there are no blocks inserted

Sometimes due to some error (mostly network) if may
not fetch any data when indexing block. If block cache update
is triggered it fails.

This PR check if list is passed to cache update function.

apps/indexer/lib/indexer/block/fetcher.ex

@@ -183,7 +183,7 @@ defmodule Indexer.Block.Fetcher do
     end
   end
 
-  defp update_block_cache(blocks) do
+  defp update_block_cache(blocks) when is_list(blocks) do
     max_block = Enum.max_by(blocks, fn block -> block.number end)
     min_block = Enum.min_by(blocks, fn block -> block.number end)
 
@@ -192,6 +192,8 @@ defmodule Indexer.Block.Fetcher do
     BlocksCache.update(blocks)
   end
 
+  defp update_block_cache(_), do: :ok
+
   defp update_transactions_cache(transactions) do
     Transactions.update(transactions)
   end