Don't bail out on files without dependencies field

python/lib/dependabot/python/file_parser/pyproject_files_parser.rb

@@ -25,7 +25,7 @@ def initialize(dependency_files:)
         def dependency_set
           dependency_set = Dependabot::FileParsers::Base::DependencySet.new
 
-          dependency_set += pyproject_dependencies
+          dependency_set += pyproject_dependencies if using_poetry? || using_pep621?
           dependency_set += lockfile_dependencies if lockfile
 
           dependency_set
@@ -38,7 +38,7 @@ def dependency_set
         def pyproject_dependencies
           if using_poetry?
             poetry_dependencies
-          elsif using_pep621?
+          else
             pep621_dependencies
           end
         end

python/spec/dependabot/python/file_parser/pyproject_files_parser_spec.rb

@@ -255,6 +255,14 @@
       end
     end
 
+    context "without dependencies" do
+      let(:pyproject_fixture_name) { "no_dependencies.toml" }
+
+      subject(:dependencies) { parser.dependency_set.dependencies }
+
+      its(:length) { is_expected.to eq(0) }
+    end
+
     context "with dependencies with empty requirements" do
       let(:pyproject_fixture_name) { "no_requirements.toml" }
 

python/spec/fixtures/pyproject_files/no_dependencies.toml

@@ -0,0 +1,10 @@
+[build-system]
+requires = ["flit_core >=3.2,<4"]
+build-backend = "flit_core.buildapi"
+
+[project]
+name = "pkgtest"
+authors = [{name = "Sample", email = "sample.project@example.org"}]
+license = {file = "LICENSE"}
+classifiers = ["License :: OSI Approved :: MIT License"]
+dynamic = ["version", "description"]