Fix BlocksTransactionsMismatch temporary fetcher

This solves a problem that was found with this fetcher:
block with no transactions were not taken into account, so they were not checked and never had their `refetch_needed` field set to false.

CHANGELOG.md

@@ -38,6 +38,7 @@
 - [#1966](https://github.com/poanetwork/blockscout/pull/1966) - fix: add fields for contract filter performance
 - [#2008](https://github.com/poanetwork/blockscout/pull/2008) - add new function clause for xDai network beneficiaries
 - [#2009](https://github.com/poanetwork/blockscout/pull/2009) - addresses page improvements
+- [#2027](https://github.com/poanetwork/blockscout/pull/2027) - fix: `BlocksTransactionsMismatch` ignoring blocks without transactions
 
 ### Chore
 

apps/indexer/lib/indexer/temporary/blocks_transactions_mismatch.ex

@@ -51,7 +51,7 @@ defmodule Indexer.Temporary.BlocksTransactionsMismatch do
   def init(initial, reducer, _) do
     query =
       from(block in Block,
-        join: transactions in assoc(block, :transactions),
+        left_join: transactions in assoc(block, :transactions),
         where: block.consensus and block.refetch_needed,
         group_by: block.hash,
         select: {block, count(transactions.hash)}
@@ -81,14 +81,19 @@ defmodule Indexer.Temporary.BlocksTransactionsMismatch do
   defp run_blocks(%Blocks{blocks_params: []}, blocks_data), do: {:retry, blocks_data}
 
   defp run_blocks(
-         %Blocks{transactions_params: transactions_params},
+         %Blocks{transactions_params: transactions_params, blocks_params: blocks_params},
          blocks_data
        ) do
-    found_blocks_map =
+    blocks_with_transactions_map =
       transactions_params
       |> Enum.group_by(&Map.fetch!(&1, :block_hash))
       |> Map.new(fn {block_hash, trans_lst} -> {block_hash, Enum.count(trans_lst)} end)
 
+    found_blocks_map =
+      blocks_params
+      |> Map.new(&{Map.fetch!(&1, :hash), 0})
+      |> Map.merge(blocks_with_transactions_map)
+
     {found_blocks_data, missing_blocks_data} =
       Enum.split_with(blocks_data, fn {block, _trans_num} ->
         Map.has_key?(found_blocks_map, to_string(block.hash))