Fixes ActionView::Template::Error: undefined method `text?` for nil:NilClass

changelogs/unreleased/25251-actionview-template-error-undefined-method-text-for-nil-nilclass.yml

+---
+title: 'Fixes "ActionView::Template::Error: undefined method `text?` for nil:NilClass"
+  on MR pages'
+merge_request: 
+author: 

lib/gitlab/diff/file_collection/merge_request_diff.rb

@@ -61,7 +61,7 @@ module Gitlab
         end
         def cacheable?(diff_file)
-          @merge_request_diff.present? && diff_file.blob.text?
+          @merge_request_diff.present? && diff_file.blob && diff_file.blob.text?
         end
         def cache_key

spec/lib/gitlab/diff/file_collection/merge_request_diff_spec.rb

@@ -10,4 +10,12 @@ describe Gitlab::Diff::FileCollection::MergeRequestDiff do
     described_class.new(merge_request.merge_request_diff, diff_options: nil).diff_files
   end
+
+  it 'does not hightlight file if blob is not accessable' do
+    allow_any_instance_of(Gitlab::Diff::File).to receive(:blob).and_return(nil)
+
+    expect_any_instance_of(Gitlab::Diff::File).not_to receive(:highlighted_diff_lines)
+
+    described_class.new(merge_request.merge_request_diff, diff_options: nil).diff_files
+  end
 end