Caused by: java.lang.IllegalArgumentException: Unable to create @Body converter for class com.iclienttech.ict_3.farm.models.LoginDetails (parameter #1)

compile 'com.squareup.retrofit2:retrofit:2.0.2'
compile 'com.squareup.okhttp3:logging-interceptor:3.2.0'
compile 'com.squareup.retrofit2:converter-gson:2.0.0-beta3'

public interface LoginAPI {
    @POST("/farm/login_screen.php")
    Call<LoginAPIResponse> userDetails (@Body LoginDetails user);
}

userId = userEmailId.getText().toString();
                password = userPassword.getText().toString();
                final LoginDetails user = new LoginDetails();
                user.setEmailId(userId);
                user.setPassword(password);
                loginAPIResponses = new LoginAPIResponse();
                AsyncTask performLogin = new AsyncTask() {
                    @Override
                    protected Object doInBackground(Object[] params) {
                        loginAPIResponses = FarmUtils.getInstance().postUserDetails(user);
                        return null;
                    }
                };
                performLogin.execute();
//Utils.Class
public LoginAPIResponse postUserDetails(LoginDetails user) {
        HttpLoggingInterceptor interceptor = new HttpLoggingInterceptor();
        interceptor.setLevel(HttpLoggingInterceptor.Level.BODY);
        OkHttpClient client = new OkHttpClient.Builder().addInterceptor(interceptor).build();
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl(farmURL)
                .addConverterFactory(GsonConverterFactory.create())
                .client(client)
                .build();
        LoginAPI loginAPI = retrofit.create(LoginAPI.class);
        try {
            Response<LoginAPIResponse> response = loginAPI.userDetails(user).execute();
            apiResponse = response.body();
        } catch (IOException e) {
            e.printStackTrace();
        }
        return apiResponse;
    }

public class LoginDetails {

    @SerializedName("email_id")
    @Expose
    private String emailId;
    @SerializedName("password")
    @Expose
    private String password;

    /**
     *
     * @return
     * The emailId
     */
    public String getEmailId() {
        return emailId;
    }

    /**
     *
     * @param emailId
     * The email_id
     */
    public void setEmailId(String emailId) {
        this.emailId = emailId;
    }

    /**
     *
     * @return
     * The password
     */
    public String getPassword() {
        return password;
    }

    /**
     *
     * @param password
     * The password
     */
    public void setPassword(String password) {
        this.password = password;
    }

}