Fix proposal export error with deleted users

app/lib/decidim/overrides/proposals/proposal_serializer.rb

@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module Decidim
+  module Overrides
+    module Proposals
+      module ProposalSerializer
+        private
+
+        def author_url(author)
+          if author.respond_to?(:nickname)
+            profile_url(author) # is a Decidim::User or Decidim::UserGroup
+          elsif author.respond_to?(:title)
+            meeting_url(author) # is a Decidim::Meetings::Meeting
+          else
+            root_url # is a Decidim::Organization
+          end
+        end
+
+        def profile_url(author)
+          return "" if author.respond_to?(:deleted?) && author.deleted?
+
+          Decidim::Core::Engine.routes.url_helpers.profile_url(author.nickname, host:)
+        end
+      end
+    end
+  end
+end

config/initializers/decidim_overrides.rb

@@ -6,6 +6,7 @@
   Decidim::SearchResourceFieldsMapper.prepend(Decidim::Overrides::SearchResourceFieldsMapper)
   Decidim::Initiatives::InitiativeMetadataGCell.include(Decidim::Initiatives::InitiativeMetadataGCellOverride)
   Decidim::Forms::UserAnswersSerializer.prepend(Decidim::Overrides::Forms::UserAnswersSerializer)
+  Decidim::Proposals::ProposalSerializer.prepend(Decidim::Overrides::Proposals::ProposalSerializer)
   Decidim::Initiative.include(Decidim::InitiativeOverride)
   Decidim::Accountability::Result.include(Decidim::Accountability::ResultOverride)
   Decidim::Accountability::ResultsCalculator.include(Decidim::Accountability::ResultsCalculatorOverride)

spec/lib/overrides_spec.rb

@@ -114,6 +114,7 @@
   {
     package: "decidim-proposals",
     files: {
+      "/lib/decidim/proposals/proposal_serializer.rb" => "ea339213f4f296aaafa3708dcd5c37c4", # remove once the solution of this PR is present https://github.com/decidim/decidim/pull/13592
       "/app/helpers/decidim/proposals/application_helper.rb" => "c17dd875a166cd0cd3c09b0e596ebef5",
       "/app/presenters/decidim/proposals/proposal_presenter.rb" => "bbc7cee02125c1f8cf909219e48af337"
     }