fix(crons): Log debug message when monitor config interval unit is invalid

sentry-ruby/lib/sentry/cron/monitor_config.rb

@@ -35,7 +35,15 @@ def self.from_crontab(crontab, **options)
       end
 
       def self.from_interval(num, unit, **options)
-        return nil unless MonitorSchedule::Interval::VALID_UNITS.include?(unit)
+        unless MonitorSchedule::Interval::VALID_UNITS.include?(unit)
+          if Sentry.initialized?
+            Sentry.sdk_logger.debug(LOGGER_PROGNAME) do
+              "Invalid interval unit #{unit.inspect} for monitor config, must be one of #{MonitorSchedule::Interval::VALID_UNITS.inspect}"
+            end
+          end
+
+          return nil
+        end
 
         new(MonitorSchedule::Interval.new(num, unit), **options)
       end

sentry-ruby/spec/sentry/cron/monitor_config_spec.rb

@@ -25,6 +25,21 @@
       expect(described_class.from_interval(5, :bla)).to eq(nil)
     end
 
+    it 'logs a debug message without valid unit' do
+      string_io = StringIO.new
+      Sentry.configuration.sdk_logger = Logger.new(string_io)
+
+      described_class.from_interval(5, :bla)
+
+      expect(string_io.string).to include("Invalid interval unit :bla for monitor config")
+    end
+
+    it 'returns nil without valid unit when SDK is not initialized' do
+      allow(Sentry).to receive(:initialized?).and_return(false)
+
+      expect(described_class.from_interval(5, :bla)).to eq(nil)
+    end
+
     it 'has correct attributes' do
       subject = described_class.from_interval(
         5,