Guard null in candidate class detection

Prevent a potential NullPointerException by returning false when `isCandidateClass` receives `null`. Added a focused unit test for `isCandidateClass` covering null, primitive/wrapper, enum, `java.lang` type, and a positive custom-class case.

Author: mercyblitz

microsphere-spring-boot-core/src/main/java/io/microsphere/spring/boot/context/properties/bind/ConfigurationPropertiesBeanContext.java

@@ -562,6 +562,9 @@ static boolean isCandidateProperty(PropertyDescriptor descriptor) {
      * @return {@code true} if the class is a binding candidate, {@code false} otherwise
      */
     static boolean isCandidateClass(Class<?> beanClass) {
+        if (beanClass == null) {
+            return false;
+        }
         if (isPrimitiveOrWrapper(beanClass) || beanClass.isEnum()) {
             return false;
         }

microsphere-spring-boot-core/src/test/java/io/microsphere/spring/boot/context/properties/bind/ConfigurationPropertiesBeanContextTest.java

@@ -31,8 +31,10 @@
 import org.springframework.core.annotation.AnnotationAttributes;
 
 import java.beans.PropertyDescriptor;
+import java.util.concurrent.TimeUnit;
 
 import static io.microsphere.spring.boot.context.properties.bind.ConfigurationPropertiesBeanContext.getInstance;
+import static io.microsphere.spring.boot.context.properties.bind.ConfigurationPropertiesBeanContext.isCandidateClass;
 import static io.microsphere.spring.boot.context.properties.bind.ConfigurationPropertiesBeanContext.isCandidateProperty;
 import static io.microsphere.spring.core.annotation.AnnotationUtils.getAnnotationAttributes;
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -151,6 +153,21 @@ void testIsCandidateProperty() {
         assertFalse(isCandidateProperty(descriptor));
     }
 
+    @Test
+    void testIsCandidateClass() {
+        // null
+        assertFalse(isCandidateClass(null));
+        // primitive type and wrapper type are not candidate class
+        assertFalse(isCandidateClass(int.class));
+        assertFalse(isCandidateClass(Integer.class));
+        // enumeration type
+        assertFalse(isCandidateClass(TimeUnit.class));
+        // String is candidate class,but is under java.lang package.
+        assertFalse(isCandidateClass(String.class));
+        // current class
+        assertTrue(isCandidateClass(getClass()));
+    }
+
     public void setName(String name) {
         // Just for testing purpose
     }