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C#: null warning even though it's not possible

Ok so here I have this function that can return a null value in some cases. However, even when testing if it is before, it still says it might be null.
My code:
if (Account.FindAccount(usernameInput) == null) { return; }
if (Account.FindAccount(usernameInput).password == "1234") // warning CS8602: Dereference of a possibly null reference
{
//Do stuff
}

Is that FindAccount operation guaranteed to be idempotent? The compiler has no such guarantee. What it returns in one call it might not return in another.
More to the point... If you believe it will always return the same result for the same input, why are you invoking it twice? Just invoke it once and store the result:
var account = Account.FindAccount(usernameInput);
if (account == null) { return; }
if (account.password == "1234")
{
//Do stuff
}

Multiple component references in an if/then logic statements in Unity?

How do you make multiple component references in a single if/then logic statements in Unity? I thought it would look something like this:
if(other.GetComponent<Component1>() != null || (GetComponent2>() != null)
{
//Run code
}
Such code returns this error:
error CS1026: ) expected

You are missing a get for the second component and a close )
if(other.GetComponent<Component1>() != null || other.GetComponent<Component2>() != null)
{
//Run code
}
With out knowing more, this is a start

Why does the else statement not get executed if one of the bool parameters for if is null?

I have this code snippet here:
public void ReDrawParallelLines(string lineName, string viewType)
{
var referenceLineOne = GetLineParams(viewType + ReferenceEnum.One.ToString() + linename);
var referenceLineTwo = GetLineParams(viewType + ReferenceEnum.Two.ToString() + linename);
if (lineName == referenceLineOne.lineParams.lineName)
{
//Do certain action with referencelineone
}
else if (lineName == referenceLineTwo.lineParams.lineName)
{
//Do same action but with referencelinetwo
}
}
I noticed that if referenceLineOne is null but I have referenceLineTwo, the else statement never gets executed. I'm not sure why? Doesn't it work such that if the bool fails the if then continue to the else and it should pass for the else. It just skips the inside if statement and the else condition entirely because the referenceLineOne is null. Why and how can I correct this check?
Basically, I am passing a line name and I want to check to see if it's equal to one of two lines I get from the GetLineParams function.

Since referenceLineOne is null, you will get an exception, which is why it bypasses the else if and jumps somewhere else.
You should do null checking like this
if (referenceLineOne != null && lineName == referenceLineOne.lineParams.lineName)
{
//Do certain action with referencelineone
}
or this if you use c#6
if (lineName == referenceLineOne?.lineParams.lineName)
{
//Do certain action with referencelineone
}

Azure MobileService Null Reference Exception

I'm currently developing an app for windows phone 8.1 with Azure. (I wouldn't really recommend this to you after my experiences). Anyway... I've got Multiple Controller classes in it who really do the same (Check if something in my database already exists and if not it creates it). The problem I have has to be in the Read() function which checks the database if an entry already exists:
public async void Read(Device device)
{
IMobileServiceTable mobileServiceTable = Connect();
MobileServiceCollection<Device, Device> devices = null;
try
{
devices = await mobileServiceTable.MobileServiceClient.GetTable<Device>().Where(d => d.Manufacturer == device.Manufacturer && d.Model == device.Model).ToCollectionAsync();
}
catch (Exception e)
{
if (_onDeviceControllerListener != null)
{
_onDeviceControllerListener.OnError(ControllerError.Error.ReadFromDatabase, e.ToString());
}
return;
}
if (_onDeviceControllerListener != null && devices != null)
{
_onDeviceControllerListener.OnRead(devices);
}
}
This one works perfectly how it should but the oder one which is basically just a copy throws a NullReferenceException by the line "apps = await mobileServiceTab...":
public async void Read(Model.App app)
{
IMobileServiceTable mobileServiceTable = Connect();
MobileServiceCollection<Model.App, Model.App> apps = null;
try {
apps = await mobileServiceTable.MobileServiceClient.GetTable<Model.App>().Where(a => a.HardwareId == app.HardwareId && a.PackageId == app.PackageId).ToCollectionAsync();
}
catch (Exception e)
{
if (_onAppControllerListener != null)
{
_onAppControllerListener.OnError(ControllerError.Error.ReadFromDatabase, e.ToString());
}
return;
}
if (_onAppControllerListener != null)
{
_onAppControllerListener.OnRead(apps);
}
}
Does somebody know what the problem is?
Thanks for helping

You can add a try...catch block and check for the "MobileServiceInvalidOperationException" exception. Also take a look at the callstack to find out what's happening.
A fiddler trace would also let you know if you made a successful call to the Mobile Service to retrieve the data. Then you can determine if the issue lies in how you handle the data in your code.
Take another look at your MobileServiceContext class and ensure all properties are accounted for especially the properties that use the "Model.App" class. E.g
public virtual DbSet<Model.App> SomeProperty { get; set; }
Hope this helps.

NullRefrenceException was unhandled by user code

Code below is placed in page_Load. How I should handle this to bypass UrlReferrer when you enter page directly first time and there is no referrer?
What I am missing here?
if (HttpContext.Current.Request.UrlReferrer.AbsoluteUri != null)
{
urlReferer = HttpContext.Current.Request.UrlReferrer.AbsoluteUri.ToString();
}
else
{
urlReferer = "";
}

Just check UrlReferrerfor null:
if (HttpContext.Current.Request.UrlReferrer != null
&& HttpContext.Current.Request.UrlReferrer.AbsoluteUri != null)
{
urlReferer = HttpContext.Current.Request.UrlReferrer.AbsoluteUri.ToString();
}
else
{
urlReferer = "";
}

Who says the client passed by the referrer in the HTTP request?
Check if UrlReferrer is null first
if (HttpContext.Current.Request.UrlReferrer != null)
{
urlReferer = HttpContext.Current.Request.UrlReferrer.AbsoluteUri.ToString();
}
else
{
urlReferer = "";
}

Why not this way much cleaner than checking nulls
private void Page_Load()
{
if (!IsPostBack)
{
if (HttpContext.Current.Request.UrlReferrer != null)
{
urlReferer = HttpContext.Current.Request.UrlReferrer.AbsoluteUri.ToString();
}
else
{
urlReferer = "";
}
}
}

I believe you need to check if HttpContext.Current.Request.UrlReferrer != null.

If UrlReferrer is null, then the test to AbsolutUri will fail.
Try initially testing UrlReferrer for null, this will probably correct the issue.

Use your debugger. If you're running this out of visual studio, than you might be brought to a debugger window when the exception is thrown. There are multiple tabs at the bottom of the debugger including "Locals" and "Watch" you can use those to see what variables are being stored.
If the above code is indeed what's causing the problem than
HttpContext.Current.Request.UrlReferrer.AbsoluteUri
or
HttpContext.Current.Request.UrlReferrer
or
HttpContext.Current.Request
or
HttpContext.Current
or
HttpContext
is set to null