diff --git a/devolo_plc_api/device.py b/devolo_plc_api/device.py
index 127084e..2915020 100644
--- a/devolo_plc_api/device.py
+++ b/devolo_plc_api/device.py
@@ -165,10 +165,10 @@ def _state_change(self, zeroconf: Zeroconf, service_type: str, name: str, state_
 
     @staticmethod
     def info_from_service(service_info: ServiceInfo) -> Optional[Dict]:
-        """Return prepared info from mDNS entries."""
+        """ Return prepared info from mDNS entries. """
         properties = {}
         if not service_info.addresses:
-            return  # No need to continue, if there is no IP address to contact the device
+            return None  # No need to continue, if there is no IP address to contact the device
 
         total_length = len(service_info.text)
         offset = 0
diff --git a/devolo_plc_api/network/__init__.py b/devolo_plc_api/network/__init__.py
index c278dc7..c58f3c2 100644
--- a/devolo_plc_api/network/__init__.py
+++ b/devolo_plc_api/network/__init__.py
@@ -11,6 +11,11 @@
 
 
 async def async_discover_network() -> Dict[str, Device]:
+    """
+    Discover all devices that expose the devolo device API via mDNS asynchronous.
+
+    :return: Devices accessible via serial number.
+    """
     browser = ServiceBrowser(Zeroconf(), "_dvl-deviceapi._tcp.local.", [_add])
     await asyncio.sleep(3)
     browser.cancel()
@@ -19,6 +24,11 @@ async def async_discover_network() -> Dict[str, Device]:
 
 
 def discover_network() -> Dict[str, Device]:
+    """
+    Discover devices that expose the devolo device API via mDNS synchronous.
+
+    :return: Devices accessible via serial number.
+    """
     browser = ServiceBrowser(Zeroconf(), "_dvl-deviceapi._tcp.local.", [_add])
     time.sleep(3)
     browser.cancel()