hide attribute with null value using leaflet

http://jsbin.com/hinekaj/edit?html,output

this is a link to a map am working on. It will be great if someone could help me to hide the attributes that have "null" as their value. I am aware that I need to use the IF command but have been struggling with it.

        onEachFeature: function (feature, layer) {
          layer.bindPopup('Address: '+ feature.properties.address 
                          + '
Sample 1: '+ feature.properties.sample_1 + ' Pb'
                          + "
Sample 1: "+ feature.properties.sample_1 + ' Pb'
                        + " , Sample 2: "+ feature.properties.sample_2 + ' Pb'
                         + "
Sample 3: "+ feature.properties.sample_3 + ' Pb'

                         + " , Sample 4: "+ feature.properties.sample_4 + ' Pb'
                         + '
Sample 5: '+ feature.properties.sample_5 + ' Pb'
                         + ' , Sample 6: '+ feature.properties.sample_6 + ' Pb'
                         + '
Sample 7: '+ feature.properties.sample_7 + ' Pb'
                         + ' , Sample 8: '+ feature.properties.sample_8 + ' Pb'
                         + '
Sample 9: '+ feature.properties.sample_9 + ' Pb'
                         + ' , Sample 10: '+ feature.properties.sample_10 + ' Pb'
                         + '
Sample 11: '+ feature.properties.sample_11 + ' Pb'
                         + ' , Sample 12: '+ feature.properties.sample_12 + ' Pb'
                         + '
Sample 13: '+ feature.properties.sample_13 + ' Pb'

                         + ' , Sample 14: '+ feature.properties.sample_14 + ' Pb'

         ); 
        },