Fix DebugExceptions crash on nil Exception#annoted_source_code

The issue was reported in #29537. We expect Exception#annoted_source_code
to return an `Array`, but this contract may not be followed by all the
implementers.

Fixes #29537.

actionpack/lib/action_dispatch/middleware/debug_exceptions.rb

@@ -134,6 +134,7 @@ module ActionDispatch
 
       def log_error(request, wrapper)
         logger = logger(request)
+
         return unless logger
 
         exception = wrapper.exception
@@ -152,10 +153,14 @@ module ActionDispatch
       end
 
       def log_array(logger, array)
+        lines = Array(array)
+
+        return if lines.empty?
+
         if logger.formatter && logger.formatter.respond_to?(:tags_text)
-          logger.fatal array.join("\n#{logger.formatter.tags_text}")
+          logger.fatal lines.join("\n#{logger.formatter.tags_text}")
         else
-          logger.fatal array.join("\n")
+          logger.fatal lines.join("\n")
         end
       end
 

actionpack/test/dispatch/debug_exceptions_test.rb

@@ -20,6 +20,12 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
   class Boomer
     attr_accessor :closed
 
+    class NilAnnotedSourceCodeError < StandardError
+      def annoted_source_code
+        nil
+      end
+    end
+
     def initialize(detailed = false)
       @detailed = detailed
       @closed = false
@@ -48,6 +54,10 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
       end
     end
 
+    def method_that_raises_nil_annoted_source_code
+      raise NilAnnotedSourceCodeError, "nil annoted_source_code"
+    end
+
     def call(env)
       env["action_dispatch.show_detailed_exceptions"] = @detailed
       req = ActionDispatch::Request.new(env)
@@ -106,6 +116,8 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
         raise_nested_exceptions
       when %r{/actionable_error}
         raise CustomActionableError
+      when %r{/nil_annoted_source_code_error}
+        method_that_raises_nil_annoted_source_code
       else
         raise "puke!"
       end
@@ -662,4 +674,16 @@ class DebugExceptionsTest < ActionDispatch::IntegrationTest
     assert_response 400
     assert_match "ActionController::BadRequest", body
   end
+
+  test "debug exceptions with misbehaving Exception#annoted_source_code" do
+    @app = DevelopmentApp
+
+    io = StringIO.new
+    logger = ActiveSupport::Logger.new(io)
+
+    get "/nil_annoted_source_code_error", headers: { "action_dispatch.show_exceptions" => true, "action_dispatch.logger" => logger }
+
+    assert_select "header h1", /DebugExceptionsTest::Boomer::NilAnnotedSourceCodeError/
+    assert_select "#container h2", /nil annoted_source_code/
+  end
 end