Fix parsing of empty sources in cobertura

changelogs/unreleased/eb-fix-cobertura-empty-sources.yml

+---
+title: Fix cobertura parser when there is an empty sources node
+merge_request: 50971
+author:
+type: fixed

lib/gitlab/ci/parsers/coverage/cobertura.rb

@@ -36,7 +36,7 @@ module Gitlab
           end
 
           def parse_node(key, value, coverage_report, context)
-            if key == 'sources' && value['source'].present?
+            if key == 'sources' && value && value['source'].present?
               parse_sources(value['source'], context)
             elsif key == 'package'
               Array.wrap(value).each do |item|

spec/lib/gitlab/ci/parsers/coverage/cobertura_spec.rb

@@ -224,6 +224,12 @@ RSpec.describe Gitlab::Ci::Parsers::Coverage::Cobertura do
         it_behaves_like 'ignoring sources, project_path, and worktree_paths'
       end
 
+      context 'when there is an empty <sources>' do
+        let(:sources_xml) { '<sources />' }
+
+        it_behaves_like 'ignoring sources, project_path, and worktree_paths'
+      end
+
       context 'when there is a <sources>' do
         context 'and has a single source with a pattern for Go projects' do
           let(:project_path) { 'local/go' } # Make sure we're not making false positives