Allow addresses to present zero balances when they do not have a balance

lib/explorer/credit.ex

@@ -23,4 +23,5 @@ defmodule Explorer.Credit do
   def refresh do
     SQL.query!(Repo, "REFRESH MATERIALIZED VIEW CONCURRENTLY credits;", [], timeout: 120_000)
   end
+  def null, do: %__MODULE__{value: Decimal.new(0), count: 0}
 end

lib/explorer/debit.ex

@@ -23,4 +23,5 @@ defmodule Explorer.Debit do
   def refresh do
     SQL.query!(Repo, "REFRESH MATERIALIZED VIEW CONCURRENTLY debits;", [], timeout: 120_000)
   end
+  def null, do: %__MODULE__{value: Decimal.new(0), count: 0}
 end

lib/explorer/forms/address_form.ex

@@ -1,8 +1,13 @@
 defmodule Explorer.AddressForm do
   @moduledoc false
 
+  alias Explorer.Credit
+  alias Explorer.Debit
+
   def build(address) do
-    balance = Decimal.sub(address.credit.value, address.debit.value)
+    credit = address.credit || Credit.null
+    debit = address.debit || Debit.null
+    balance = Decimal.sub(credit.value, debit.value)
     Map.put(address, :balance, balance)
   end
 end

test/explorer/forms/address_form_test.exs

@@ -6,7 +6,7 @@ defmodule Explorer.AddressFormTest do
   alias Explorer.Debit
 
   describe "build/1" do
-    test "that it has a balance" do
+    test "returns a balance" do
       address = insert(:address, %{hash: "bert"})
       insert(:transaction, value: 5) |> with_addresses(%{to: "bert", from: "ernie"})
       insert(:transaction, value: 5) |> with_addresses(%{to: "bert", from: "kermit"})
@@ -15,5 +15,13 @@ defmodule Explorer.AddressFormTest do
       Debit.refresh
       assert AddressForm.build(Repo.preload(address, [:debit, :credit])).balance == Decimal.new(10)
     end
+
+    test "returns a zero balance when the address does not have balances" do
+      address = insert(:address, %{hash: "bert"})
+      insert(:transaction, value: 5) |> with_addresses(%{to: "bert", from: "ernie"})
+      insert(:transaction, value: 5) |> with_addresses(%{to: "bert", from: "kermit"})
+
+      assert AddressForm.build(Repo.preload(address, [:debit, :credit])).balance == Decimal.new(0)
+    end
   end
 end