title: I enter 0 but ExtJS saves null to DB
body: <p>When I enter 0 into my ExtJS input field (ie. numberfield) When I save the form I get null on the way to the DB. I there any special setting I need to enable in order for 0 to treated like 0 and not like null?</p>
  
  <p>Here's my field's code:</p>
  
  <pre><code>{
                          xtype: 'numberfield',
                          itemId: 'testField',
                          id: 'testField',
                          fieldLabel: "testField",
                          fieldStyle: 'text-align: right;',
                          labelWidth: 320,
                          labelAlign: 'right',
                          decimalPrecision: Ext.util.Format.currencyPrecision,
                          allowBlank: true,
                          allowDecimals: true,
                          minValue: 0,
                          maxValue: 999.9999,
                          defaultValue: null,
                          allowNull: true,
                          hideTrigger: true,
                          keyNavEnabled: false,
                          mouseWheelEnabled: false
                      },
  </code></pre>