Editing Data in modal form

Question

I have an mxml for my project, in which I have a DataGrid with a few fields, just enough to locate a desired record.  When I double click on the item in the DataGrid, a modal form pops up, populated with the data in all the fields of the same record.  So far, so good.  However, now when I try to edit any data in any field, I get an error message:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at mx.containers::TabNavigator/keyDownHandler()[E:\dev\gumbo_beta2\frameworks\projects\frame work\src\mx\containers\TabNavigator.as:904]
I don't have a keyDownHandler on my TabNavigator.
My project is fairly small and a knowledgable person would probably be able to see my mistake in 10 seconds or less if they reviewed my code.  A zip file with my code is attached.
If some one could take a look, and post the errorneous line in the reply... then everyone in the forum could benefit.
I am making progress thanks to the excellent examples and instructions provided at:
http://sujitreddyg.wordpress.com/flash-builder-4/
I got a little demo of my own working just like in the instructions.  I had to rebuild my test project from scratch several times.. I think the FB 4 b 1 stuff was interfering with the FB 4 b2 way of doing things. However now, I am trying to build my test project in the way that my real project will work.. and that is... all detail forms will be opened in a modal window, edited, commited and then closed.

Answer 1

PROBLEM:  MODAL "frmSBJ" FORM crashes when I try to edit the text in a TextInput.  (See exact error text in previous post)
In the baa_ria.mxml: ------------------------------------------------------
    <fx:Script>
        <![CDATA[
            import components.*;
            import mx.managers.PopUpManager;
            protected function grdSBJs_itemDoubleClickHandler(event:ListEvent):void
                show_frmSBJ();               
            public function show_frmSBJ():void
                var pop:frmSBJ = frmSBJ(PopUpManager.createPopUp(this, frmSBJ, true));
                pop.bAA_SBJ = grdSBJs.selectedItem as BAA_SBJ;
                PopUpManager.centerPopUp(pop);                                          
In the "components" folder, frmSBJ.mxml: ---------------------------------------------------------
<?xml version="1.0" encoding="utf-8"?>
<s:Group xmlns:fx="http://ns.adobe.com/mxml/2009"
                 xmlns:s="library://ns.adobe.com/flex/spark"
                 xmlns:mx="library://ns.adobe.com/flex/halo"
                 width="600" height="506"
                 xmlns:valueObjects="valueObjects.*"
                 xmlns:baa_data_svc="services.baa_data_svc.*">
    <s:layout>
        <s:BasicLayout/>
    </s:layout>
    <fx:Script>
        <![CDATA[
            import mx.controls.Alert;
            import mx.managers.PopUpManager;
            protected function btnDone_clickHandler(event:MouseEvent):void
                // TODO: Refresh the grdSBJs somehow
                PopUpManager.removePopUp(this);
            protected function btnCommit_clickHandler(event:MouseEvent):void
                updt_SBJResult.token = baa_data_svc.updt_SBJ(bAA_SBJ);
        ]]>
    </fx:Script>
    <fx:Declarations>
        <valueObjects:BAA_SBJ id="bAA_SBJ"/>
        <mx:DateFormatter id="dfISO" formatString="YYYY-MM-DD"/>
        <mx:DateFormatter id="tfHMS" formatString="HH:MM:SS"/>
        <s:CallResponder id="updt_SBJResult"/>
        <baa_data_svc:Baa_data_svc id="baa_data_svc" fault="Alert.show(event.fault.faultString + '\n' + event.fault.faultDetail)" showBusyCursor="true"/>
    </fx:Declarations>
    <s:Panel x="15" y="9" width="564" height="465" id="pnlMain" title="Subject Name">
        <s:Group x="10" y="377" width="544" height="41" id="grpButtonBar">
            <s:Button x="309" y="10" label="Commit" id="btnCommit" click="btnCommit_clickHandler(event)" />
            <s:Button x="386" y="10" label="Undo" id="btnUndo"/>
            <s:Button x="464" y="10" label="Done" click="btnDone_clickHandler(event)" id="btnDone"/>
        </s:Group>
        <mx:TabNavigator x="6" y="8" width="548" height="361" id="tnvSBJ" creationPolicy="all">
            <s:NavigatorContent label="Properties" width="100%" height="100%" id="nvcProperties">
                <mx:Form x="126" y="5">
                    <mx:FormItem label="SBJ_NM">
                        <s:TextInput id="sBJ_NMTextInput" text="@{bAA_SBJ.SBJ_NM}"/>
                    </mx:FormItem>
                    <mx:FormItem label="SBJ_DOB">
                        <mx:DateField id="sBJ_DOBDateField" selectedDate="@{bAA_SBJ.SBJ_DOB}"/>
                    </mx:FormItem>
                    <mx:FormItem label="SBJ_ID">
                        <s:TextInput id="sBJ_IDTextInput" text="@{bAA_SBJ.SBJ_ID}"/>
                    </mx:FormItem>
                    <mx:FormItem label="NOTE">
                        <s:TextArea id="nOTETextInput" text="@{bAA_SBJ.NOTE}"/>
                    </mx:FormItem>
                </mx:Form>
            </s:NavigatorContent>
            <s:NavigatorContent label="Meta-data" width="100%" height="100%" id="nvcMetaData">
                <mx:Form x="117" y="25">
                    <mx:FormItem label="SRC_SYS_NM">
                        <mx:Text id="sRC_SYS_NMText" text="{bAA_SBJ.SRC_SYS_NM}"/>                       
                    </mx:FormItem>
                    <mx:FormItem label="SRC_SYS_GUID">
                        <mx:Text id="sRC_SYS_GUIDText" text="{bAA_SBJ.SRC_SYS_GUID}"/>
                    </mx:FormItem>
                    <mx:FormItem label="OBJ_GUID">
                        <mx:Text id="oBJ_GUIDText" text="{bAA_SBJ.OBJ_GUID}"/>
                    </mx:FormItem>
                    <mx:FormItem label="CDT">
                        <mx:Text id="cDTText" text="{dfISO.format(bAA_SBJ.CDT)}"/>
                    </mx:FormItem>
                    <mx:FormItem label="CTM">
                        <mx:Text id="cTMText" text="{tfHMS.format(bAA_SBJ.CTM)}"/>
                    </mx:FormItem>
                    <mx:FormItem label="CBY">
                        <mx:Text id="cBYText" text="{bAA_SBJ.CBY}"/>
                    </mx:FormItem>
                    <mx:FormItem label="MDT">
                        <mx:Text id="mDTText" text="{dfISO.format(bAA_SBJ.MDT)}"/>
                    </mx:FormItem>
                    <mx:FormItem label="MTM">
                        <mx:Text id="mTMText" text="{tfHMS.format(bAA_SBJ.MTM)}"/>
                    </mx:FormItem>
                    <mx:FormItem label="MBY">
                        <mx:Text id="mBYText" text="{bAA_SBJ.MBY}"/>
                    </mx:FormItem>
                </mx:Form>
            </s:NavigatorContent>
        </mx:TabNavigator>
    </s:Panel>       
</s:Group>
Thanks for your help pointing out where in this code I am going wrong.