diff --git a/src/test/java/examples/spring/LastNameParameterConverter.java b/src/test/java/examples/spring/LastNameParameterConverter.java
index f69c83b3a..2a45753d7 100644
--- a/src/test/java/examples/spring/LastNameParameterConverter.java
+++ b/src/test/java/examples/spring/LastNameParameterConverter.java
@@ -15,13 +15,15 @@
  */
 package examples.spring;
 
+import org.jspecify.annotations.NullMarked;
 import org.mybatis.dynamic.sql.ParameterTypeConverter;
 import org.springframework.core.convert.converter.Converter;
 
+@NullMarked
 public class LastNameParameterConverter implements ParameterTypeConverter<LastName, String>,
         Converter<LastName, String> {
     @Override
     public String convert(LastName source) {
-        return source == null ? null : source.getName();
+        return source.getName();
     }
 }
diff --git a/src/test/java/examples/spring/YesNoParameterConverter.java b/src/test/java/examples/spring/YesNoParameterConverter.java
index 131c0d84a..f86cc7b0f 100644
--- a/src/test/java/examples/spring/YesNoParameterConverter.java
+++ b/src/test/java/examples/spring/YesNoParameterConverter.java
@@ -15,12 +15,14 @@
  */
 package examples.spring;
 
+import org.jspecify.annotations.NullMarked;
 import org.mybatis.dynamic.sql.ParameterTypeConverter;
 
+@NullMarked
 public class YesNoParameterConverter implements ParameterTypeConverter<Boolean, String> {
 
     @Override
     public String convert(Boolean source) {
-        return source == null ? null : source ? "Yes" : "No";
+        return source ? "Yes" : "No";
     }
 }
diff --git a/src/test/kotlin/examples/kotlin/mybatis3/custom/render/KCustomRenderingTest.kt b/src/test/kotlin/examples/kotlin/mybatis3/custom/render/KCustomRenderingTest.kt
index d0c7e7a04..47a6fcaed 100644
--- a/src/test/kotlin/examples/kotlin/mybatis3/custom/render/KCustomRenderingTest.kt
+++ b/src/test/kotlin/examples/kotlin/mybatis3/custom/render/KCustomRenderingTest.kt
@@ -304,7 +304,7 @@ class KCustomRenderingTest {
         }
     }
 
-    private fun <T> dereference(column: SqlColumn<T>, attribute: String) =
+    private fun <T : Any> dereference(column: SqlColumn<T>, attribute: String) =
         SqlColumn.of<String>(column.name() + "->>'" + attribute + "'", column.table(), JDBCType.VARCHAR)
 
     companion object {