Unable to add Observer or java.lang.NullPointerException at java.util.Observable.addObserver(Observable.java:55)

Question

I am basically making my effort to add an observer to 'MUserData.ProfileDetails' from ,View_profile Activity' but i am unable to achieve it, it always gives me crash or error in 'View_profile' at line 24, any help would be appreciated.

My logcat is as follows,

    /***********************log or crash report**************************/

     Caused by: java.lang.NullPointerException                                                       at java.util.Observable.addObserver(Observable.java:55)                                                    at cl.click.ui.activities.View_Profile.initialize(View_Profile.java:24)                 at cl.click.ui.activities.View_Profile.onCreate(View_Profile.java:18)
    at android.app.Activity.performCreate(Activity.java:5231)at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)

    /*****************************MUserData*********************************/
    My Modal class is as follows,

    package cl.click.utility.modals;

    import com.fasterxml.jackson.annotation.JsonProperty;
    import com.fasterxml.jackson.annotation.JsonPropertyOrder;

    import java.util.ArrayList;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    import java.util.Observable;

    @JsonPropertyOrder({
            "data"
    })
    public class MUserData {

@JsonProperty("data")
private ProfileDetails.Data data;

@JsonProperty("data")
public ProfileDetails.Data getData() {
    return data;
}

@JsonProperty("data")
public void setData(ProfileDetails.Data data) {
    this.data = data;
}

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
        "description"
})
public class ProfileDetails extends Observable 
{
    @JsonProperty("description")
    private String description;
    @JsonProperty("description")
    public String getDescription() {
        return description;
    }
    @JsonProperty("description")
    public void setDescription(String description) {
        this.description = description;
    }
    public void setODescription(String description) {
        this.description=description;
        notifyChange(description);
    }
}
 @JsonInclude(JsonInclude.Include.NON_NULL)
    @JsonPropertyOrder({
            "profileDetails"
    })
    public class Data {
        @JsonProperty("profileDetails")
        private ProfileDetails profileDetails;
        @JsonProperty("profileDetails")
        public ProfileDetails getProfileDetails() {
            return profileDetails;
        }
        @JsonProperty("profileDetails")
        public void setProfileDetails(ProfileDetails profileDetails) {
            this.profileDetails = profileDetails;
        }
    }
}

}

    /****************************View_Profile******************************/


     package cl.click.ui.activities;
        import android.support.v7.app.AppCompatActivity;

        import java.util.Observable;
        import java.util.Observer;

        import cl.click.ApplicationClass;
        import cl.click.R;
        import cl.click.utility.modals.MUserData;

        public class View_Profile extends AppCompatActivity implements Observer
        {
            @Override
            protected void onCreate(Bundle savedInstanceState) {
                super.onCreate(savedInstanceState);
                setContentView(R.layout.activity_profile_view);

                initialize();
            }

            private final void initialize()
            {
                MUserData.ProfileDetails profileDetails=((ApplicationClass)getApplicationContext()).getProfileDetails();
                profileDetails.addObserver(this);           //Error here on setting the observer
            }

            @Override
            public void update(Observable observable, Object data) {
                LogUtil.e("data is:-",data.toString());
            }
        }

/****************************ApplicationClass******************************/

    package cl.click;

    import android.app.Application;

    import java.util.Observable;
    import java.util.Observer;

    import cl.click.utility.modals.MUserData;
    public class ApplicationClass extends Application
    {
        private MUserData.ProfileDetails profileDetails;

        @Override
        public void onCreate() {
            super.onCreate();
            profileDetails=new MUserData().new ProfileDetails();
        }

        public MUserData.ProfileDetails getProfileDetails() {
            return profileDetails;
        }

        public void setProfileDetails(MUserData.ProfileDetails profileDetails) {
            this.profileDetails = profileDetails;
        }

    }