One carriage return should be treated as a <br/> and two as a <p> when we save a document

When I write in wiki mode :

        text 1
        text 2

        text 3
        text 4

and save document . The result is :

      text 1 text 2

      text 3 text 4

We need modify this . It should be :

        text 1
        text 2

        text 3
        text 4

One carriage return should be treated as a <br/> and two as a <p> when we save a document.