Running testng.xml file shows Invoked Methods error

Following error comes out when I am running selenium with testng.xml file:

[RemoteTestNG] detected TestNG version 7.0.0   TestNG 7.0.0 by Cédric Beust (cedric@beust.com)

Invoked methods

Login.LoginPage()[pri:1, instance:jproject.Login@520a3426] 1376400422

FAILED: LoginPage java.lang.NullPointerException

While my testng.xml file is as below:

<groups>
        <run>

            <include name="Deal"  />
        </run>
    </groups>
    <classes>
          <class name="jproject.Login" />
    </classes>
</test>