diff --git a/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/channel/KNXChannelFactory.java b/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/channel/KNXChannelFactory.java
index 826ed573d00..b29a1f1c8ec 100644
--- a/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/channel/KNXChannelFactory.java
+++ b/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/channel/KNXChannelFactory.java
@@ -56,6 +56,7 @@ public final class KNXChannelFactory {
                 .map(Map.Entry::getValue).findFirst()
                 .orElseThrow(() -> new IllegalArgumentException(channelTypeUID + " is not a valid channel type ID"));
 
-        return supplier.apply(channel);
+        // typecast to avoid warning about unsafe return type; we know that the lookup returns non null values
+        return (KNXChannel) supplier.apply(channel);
     }
 }
diff --git a/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/client/SerialTransportAdapter.java b/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/client/SerialTransportAdapter.java
index 7028d4b668f..d80b5f3ee09 100644
--- a/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/client/SerialTransportAdapter.java
+++ b/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/client/SerialTransportAdapter.java
@@ -156,7 +156,9 @@ public class SerialTransportAdapter implements SerialCom {
         if (tmpSerialPortManager == null) {
             return Collections.emptyList();
         }
-        return tmpSerialPortManager.getIdentifiers().map(SerialPortIdentifier::getName).collect(Collectors.toList());
+        // typecast only required to avoid warning about less-annotated type
+        return (List<String>) tmpSerialPortManager.getIdentifiers().map(SerialPortIdentifier::getName)
+                .collect(Collectors.toList());
     }
 
     @Override
diff --git a/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/dpt/DPTUnits.java b/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/dpt/DPTUnits.java
index c6a06dda511..a550f2027bf 100644
--- a/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/dpt/DPTUnits.java
+++ b/bundles/org.openhab.binding.knx/src/main/java/org/openhab/binding/knx/internal/dpt/DPTUnits.java
@@ -116,7 +116,7 @@ public class DPTUnits {
         DPT_UNIT_MAP.put(DPTXlator2ByteUnsigned.DPT_TIMEPERIOD_100.getID(), "ms"); // according to spec, it is ms
 
         // two byte signed (DPT 8)
-        DPT_UNIT_MAP.remove(DptXlator2ByteSigned.DptValueCount.getID()); // pulses habe no unit
+        DPT_UNIT_MAP.remove(DptXlator2ByteSigned.DptValueCount.getID()); // pulses have no unit
 
         // 4 byte unsigned (DPT 12)
         DPT_UNIT_MAP.remove(DPTXlator4ByteUnsigned.DPT_VALUE_4_UCOUNT.getID()); // counts have no unit
diff --git a/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/channel/KNXChannelFactoryTest.java b/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/channel/KNXChannelFactoryTest.java
index 78aa0586de0..e6bf0a50ccb 100644
--- a/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/channel/KNXChannelFactoryTest.java
+++ b/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/channel/KNXChannelFactoryTest.java
@@ -18,6 +18,7 @@ import static org.mockito.Mockito.when;
 import static org.openhab.binding.knx.internal.KNXBindingConstants.*;
 
 import java.util.Map;
+import java.util.Objects;
 
 import org.eclipse.jdt.annotation.NonNullByDefault;
 import org.junit.jupiter.api.Test;
@@ -42,7 +43,7 @@ class KNXChannelFactoryTest {
      */
     @Test
     public void testNullChannelUidFails() {
-        Channel channel = mock(Channel.class);
+        Channel channel = Objects.requireNonNull(mock(Channel.class));
 
         assertThrows(IllegalArgumentException.class, () -> {
             KNXChannelFactory.createKnxChannel(channel);
@@ -51,7 +52,7 @@ class KNXChannelFactoryTest {
 
     @Test
     public void testInvalidChannelUidFails() {
-        Channel channel = mock(Channel.class);
+        Channel channel = Objects.requireNonNull(mock(Channel.class));
         when(channel.getChannelTypeUID()).thenReturn(new ChannelTypeUID("a:b:c"));
 
         assertThrows(IllegalArgumentException.class, () -> {
@@ -65,7 +66,7 @@ class KNXChannelFactoryTest {
             CHANNEL_NUMBER_CONTROL, CHANNEL_ROLLERSHUTTER, CHANNEL_ROLLERSHUTTER_CONTROL, CHANNEL_STRING,
             CHANNEL_STRING_CONTROL, CHANNEL_SWITCH, CHANNEL_SWITCH_CONTROL })
     public void testSuccess(String channeltype) {
-        Channel channel = mock(Channel.class);
+        Channel channel = Objects.requireNonNull(mock(Channel.class));
         Configuration configuration = new Configuration(
                 Map.of("key1", "5.001:<1/2/3+4/5/6+1/5/6", "key2", "1.001:7/1/9+1/1/2"));
         when(channel.getChannelTypeUID()).thenReturn(new ChannelTypeUID("knx:" + channeltype));
diff --git a/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/channel/KNXChannelTest.java b/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/channel/KNXChannelTest.java
index 866a1410f1c..560fbe09fce 100644
--- a/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/channel/KNXChannelTest.java
+++ b/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/channel/KNXChannelTest.java
@@ -18,6 +18,7 @@ import static org.mockito.Mockito.when;
 
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Set;
 
 import org.eclipse.jdt.annotation.NonNullByDefault;
@@ -139,7 +140,7 @@ class KNXChannelTest {
 
     @Test
     public void testChannelGaParsing() throws KNXFormatException {
-        Channel channel = mock(Channel.class);
+        Channel channel = Objects.requireNonNull(mock(Channel.class));
         Configuration configuration = new Configuration(
                 Map.of("key1", "5.001:<1/2/3+4/5/6+1/5/6", "key2", "1.001:7/1/9+1/1/2"));
         when(channel.getChannelTypeUID()).thenReturn(new ChannelTypeUID("a:b:c"));
diff --git a/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/dpt/DPTTest.java b/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/dpt/DPTTest.java
index 71c3b7ab56d..cda7f4c796c 100644
--- a/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/dpt/DPTTest.java
+++ b/bundles/org.openhab.binding.knx/src/test/java/org/openhab/binding/knx/internal/dpt/DPTTest.java
@@ -59,17 +59,16 @@ class DPTTest {
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT5ValueFromQuantityType() {
         assertEquals("80", ValueEncoder.encode(new QuantityType<>("80 %"), "5.001"));
 
         assertEquals("180", ValueEncoder.encode(new QuantityType<>("180 °"), "5.003"));
-        assertTrue(ValueEncoder.encode(new QuantityType<>("3.14 rad"), "5.003").startsWith("179."));
+        assertTrue(Objects.requireNonNullElse(ValueEncoder.encode(new QuantityType<>("3.14 rad"), "5.003"), "")
+                .startsWith("179."));
         assertEquals("80", ValueEncoder.encode(new QuantityType<>("80 %"), "5.004"));
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT7ValueFromQuantityType() {
         assertEquals("1000", ValueEncoder.encode(new QuantityType<>("1000 ms"), "7.002"));
         assertEquals("1000", ValueEncoder.encode(new QuantityType<>("1000 ms"), "7.003"));
@@ -86,7 +85,6 @@ class DPTTest {
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT8ValueFromQuantityType() {
         assertEquals("1000", ValueEncoder.encode(new QuantityType<>("1000 ms"), "8.002"));
         assertEquals("1000", ValueEncoder.encode(new QuantityType<>("1000 ms"), "8.003"));
@@ -100,7 +98,6 @@ class DPTTest {
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT9ValueFromQuantityType() {
         assertEquals("23.1", ValueEncoder.encode(new QuantityType<>("23.1 °C"), "9.001"));
         assertEquals(5.0,
@@ -109,14 +106,16 @@ class DPTTest {
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 K"), "9.002"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1000 mK"), "9.002"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 °C"), "9.002"));
-        assertTrue(ValueEncoder.encode(new QuantityType<>("1 °F"), "9.002").startsWith("0.55"));
+        assertTrue(Objects.requireNonNullElse(ValueEncoder.encode(new QuantityType<>("1 °F"), "9.002"), "")
+                .startsWith("0.55"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 K/h"), "9.003"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 °C/h"), "9.003"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1000 mK/h"), "9.003"));
         assertEquals("600", ValueEncoder.encode(new QuantityType<>("10 K/min"), "9.003"));
         assertEquals("100", ValueEncoder.encode(new QuantityType<>("100 lx"), "9.004"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 m/s"), "9.005"));
-        assertTrue(ValueEncoder.encode(new QuantityType<>("1.94 kn"), "9.005").startsWith("0.99"));
+        assertTrue(Objects.requireNonNullElse(ValueEncoder.encode(new QuantityType<>("1.94 kn"), "9.005"), "")
+                .startsWith("0.99"));
         assertEquals(1.0, Double
                 .parseDouble(Objects.requireNonNull(ValueEncoder.encode(new QuantityType<>("3.6 km/h"), "9.005"))));
         assertEquals("456", ValueEncoder.encode(new QuantityType<>("456 Pa"), "9.006"));
@@ -133,34 +132,33 @@ class DPTTest {
         assertEquals("12", ValueEncoder.encode(new QuantityType<>("12 W/m²"), "9.022"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 K/%"), "9.023"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 °C/%"), "9.023"));
-        assertTrue(ValueEncoder.encode(new QuantityType<>("1 °F/%"), "9.023").startsWith("0.55"));
+        assertTrue(Objects.requireNonNullElse(ValueEncoder.encode(new QuantityType<>("1 °F/%"), "9.023"), "")
+                .startsWith("0.55"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 kW"), "9.024"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 l/h"), "9.025"));
         assertEquals("60", ValueEncoder.encode(new QuantityType<>("1 l/min"), "9.025"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 l/m²"), "9.026"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 °F"), "9.027"));
-        assertTrue(ValueEncoder.encode(new QuantityType<>("-12 °C"), "9.027").startsWith("10."));
+        assertTrue(Objects.requireNonNullElse(ValueEncoder.encode(new QuantityType<>("-12 °C"), "9.027"), "")
+                .startsWith("10."));
         assertEquals("10", ValueEncoder.encode(new QuantityType<>("10 km/h"), "9.028"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 g/m³"), "9.029"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 µg/m³"), "9.030"));
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT10ValueFromQuantityType() {
-        // DateTimeTyype, not QuantityType
+        // DateTimeType, not QuantityType
         assertEquals("Wed, 17:30:00", ValueEncoder.encode(new DateTimeType("2019-06-12T17:30:00Z"), "10.001"));
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT11ValueFromQuantityType() {
-        // DateTimeTyype, not QuantityType
+        // DateTimeType, not QuantityType
         assertEquals("2019-06-12", ValueEncoder.encode(new DateTimeType("2019-06-12T17:30:00Z"), "11.001"));
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT12ValueFromQuantityType() {
         // 12.001: dimensionless
 
@@ -174,7 +172,6 @@ class DPTTest {
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT13ValueFromQuantityType() {
         // 13.001 dimensionless
         assertEquals("24", ValueEncoder.encode(new QuantityType<>("24 m³/h"), "13.002"));
@@ -195,7 +192,6 @@ class DPTTest {
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT14ValueFromQuantityType() {
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 m/s²"), "14.000"));
         assertEquals("1", ValueEncoder.encode(new QuantityType<>("1 rad/s²"), "14.001"));
@@ -287,9 +283,8 @@ class DPTTest {
     }
 
     @Test
-    @SuppressWarnings("null")
     void testToDPT19ValueFromQuantityType() {
-        // DateTimeTyype, not QuantityType
+        // DateTimeType, not QuantityType
         assertEquals("2019-06-12 17:30:00", ValueEncoder.encode(new DateTimeType("2019-06-12T17:30:00Z"), "19.001"));
     }
 
@@ -358,7 +353,7 @@ class DPTTest {
         assertNotEquals(DPTXlator2ByteUnsigned.DPT_TIMEPERIOD_100.getUnit(), "ms"); // according to spec, it is ms
 
         // two byte signed (DPT 8, DPTXlator is missing in calimero 2.5-M1)
-        assertNotEquals("", DptXlator2ByteSigned.DptValueCount.getUnit()); // pulses habe no unit
+        assertNotEquals("", DptXlator2ByteSigned.DptValueCount.getUnit()); // pulses have no unit
 
         // 4 byte unsigned (DPT 12)
         assertNotEquals("", DPTXlator4ByteUnsigned.DPT_VALUE_4_UCOUNT.getUnit()); // counts have no unit