PowerMockito MissingResourceException ResourceBundle

Question

im trying to test a method using
PowerMockito, this method calls ResourceBundle. this is the code of my class :

public class ClasstTotest{

    public String methodToTest(final String lang) throws IOException {
        
        final ResourceBundle i18n = ApplicationResource.getMessageBundle(lang);
        
        System.out.println(i18n.getString("mytextKey")); // the exception starts from this line
        
        // code....
        
        //return ...
    }
}

and this is my test class:

    @RunWith(PowerMockRunner.class)
    @PrepareForTest({ ApplicationResource.class})
    @PowerMockIgnore({ "javax.management.*" })
    public class ClasstTotestTest {
    
        @Before
        public void setUpMock() {
            
            PowerMockito.mockStatic(ApplicationResource.class);
        }
        
        @Test
        public void methodToTest_TEST() throws Exception {
            
            ClasstTotest classtTotestSpy = PowerMockito.spy(new ClasstTotest());
            final ResourceBundle resourceBundleMock = PowerMockito.mock(ResourceBundle.class);
            
            PowerMockito.when(ApplicationResource.getMessageBundle(any(String.class))).thenReturn(resourceBundleMock);
            
            PowerMockito.when(resourceBundleMock.getString("mytextKey")).thenReturn("my value");
            
            String result= classtTotestSpy.methodToTest("fr-FR");
// assertion...
    
        }
    }

but when i run my test i got the following error :

java.util.MissingResourceException: Can't find resource for bundle org.mockito.codegen.ResourceBundle$MockitoMock$1094973450, key mytextKey
    at java.util.ResourceBundle.getObject(ResourceBundle.java:450)
    at java.util.ResourceBundle.getString(ResourceBundle.java:407)

do you have in idea please what's the wrong with my test and why im getting "Can't find resource for bundle" error.

thanks in advance.

regards