when I added Firestore cloud dependency, my app crashes when the user logs out     kotlin.KotlinNullPointerException             at com.example.proghelp.ProfileActivity$read_write_fire$2.onEvent(ProfileActivity.kt:93)             at com.example.proghelp.ProfileActivity$read_write_fire$2.onEvent(ProfileActivity.kt:35)             at com.google.firebase.firestore.DocumentReference.zza(Unknown Source)             at com.google.firebase.firestore.zzd.onEvent(Unknown Source)             at com.google.android.gms.internal.firebase-firestore.zzkp.zza(Unknown Source)             at com.google.android.gms.internal.firebase-firestore.zzkq.run(Unknown Source)             at android.os.Handler.handleCallback(Handler.java:605)             at android.os.Handler.dispatchMessage(Handler.java:92)             at android.os.Looper.loop(Looper.java:137)             at android.app.ActivityThread.main(ActivityThread.java:4517)             at java.lang.reflect.Method.invokeNative(Native Method)             at java.lang.reflect.Method.invoke(Method.java:511)             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:993)             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:760)             at dalvik.system.NativeStart.main(Native Method)   my firebase dependencies    implementation 'com.google.firebase:firebase-core:15.0.0'     implementation 'com.google.firebase:firebase-storage:15.0.0'     implementation 'com.google.firebase:firebase-database:15.0.0'     implementation 'com.google.firebase:firebase-auth:15.0.0'     implementation 'com.google.android.gms:play-services-auth:15.0.0'     implementation 'com.firebaseui:firebase-ui-database:3.1.3'     implementation 'com.firebaseui:firebase-ui-storage:3.2.1'     implementation 'com.google.firebase:firebase-analytics:15.0.0'     implementation 'com.google.firebase:firebase-firestore:15.0.0'     implementation 'com.android.support:multidex:1.0.3'   my log is in tis code:    var db = FirebaseFirestore.getInstance();        val notebookRef3 = db.collection(currentuser.uid)   notebookRef3.document("name").addSnapshotListener { querySnapshot, e -&gt;             var note = querySnapshot!!.toObject(Note2::class.java)            var name = note!!.username             iduserprofile.text = name         }   it says the log is here      var note = querySnapshot!!.toObject(Note2::class.java)
What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?
Populating cascading dropdown lists in JSP/Servlet Setup SunFire 440 Raid Configuration How can I setup Internal Hard disk RAID5 configuration? I have SunFire 440 machine with 4 internal hard disk. I have never worked on Sun systems except for now and I am exploring google for the above solution. If anyone could help me out. Compute the (multiplicative) inverse of $4x+3$ in the field $\frac {\Bbb F_{11}[x]}{\langle x^2+1 \rangle}$? So I am finding a polynomial $px+q$ ($p,q \in \Bbb F_{11}$) which is multiplicative inverse of $4x+3$ in $\frac {\Bbb F_{11}[x]}{\langle x^2+1 \rangle}$.  i.e. $[(4x+3)+\langle x^2+1 \rangle][(px+q)+\langle x^2+1 \rangle]=1+\langle x^2+1 \rangle$   $\Rightarrow$  $(4x+3)(px+q)+\langle x^2+1 \rangle=1+\langle x^2+1 \rangle$  $\Rightarrow$  $4px^2+(4q+3p)x+3q+\langle x^2+1 \rangle=1+\langle x^2+1 \rangle$.  We see that the remainder,when $(4x+3)(px+q)$ is divided by $x^2+1$, is $1$. So by Division algorithm,  $$ \require{enclose} \begin{array}{r} 4p \\[-3pt] x^2+1 \enclose{longdiv}{4px^2+(4q+3p)x+3q} \\[-3pt] \underline{4px^2+4p} \\[-3pt] (4q+3p)x+(3q-4p) \\[-3pt] \end{array} $$    So I equate $(4q+3p)x+(3q-4p)=1$ and solve the simultaneous linear equations  $4q+3p=0, 3q-4p=1$. I get $p=6,q=1$  Hence $6x+1$ is the required inverse.  I am pretty sure that the answer is correct but is the method to achieve it right? Extrusions causing problems in edit mode When I extruded vertices in edit mode, for some reason one of the sides of my 3-D model (the textured-looking side to the right) is creating a lot of errors. First off, it automatically sets extrusions on the x-axis. Secondly, it doesn't allow me to extrude planes into 3-D shapes. Thirdly, I can't increase the height of vertices without it creating a new face. Finally, it renders those automatic textures to create a grainy black texture in render mode. I attached an image with the solid object (top) and the rendered object (bottom). Note: I did not set any textures or alter the lighting on the model. Also, the left gray side is working perfectly fine without errors. After hitting 80% LTV, my mortgage lender refuses to remove PMI. Any recourse? Participles to modify the subject of the main clause "Essos is an immense landmass located to the east of Westeros,   extending into the far east of the known world." (Here, "extending"   describes the Essos or does it describes the landmass? )   Having seen this sentence above, I question came to my mind.   Can I use participles to modify the subject of the main clause when there is no connection between main clause and participle clause. For example:      1- "He is a bookworm, living in Canada. (He is a bookworm + He lives in   Canada, there is no connection between being bookworm and living in   Canada)      2- He, living in Canada, is a book worm. (I suppose, this placement would be more correct) How do I install drivers for Realtek RTL8812BU? Effect of each parameter on a Monte Carlo Simulation I was wondering what is the best way to determine the effect of each random parameter on the result obtained from a Monte Carlo Simulation.  I realise I have asked a similar question , but this time I am making this question in a more general manner as I didn't get any answers previously.   Background: I'm essentially running a Monte Carlo Simulation where I sample randomly from 65 Normal Distributions and 2 Uniform Distributions. Then, i then input these values to a linear equation and run this for 500.000 iterations. I just wanted to determine the best way to establish the relative effect of each of these 67 (in total) random variables on the final outcome from my Monte Carlo Simulation. Importance of series resistor at output of Rectifier What is a plain English explanation of "Big O" notation? I'd prefer as little formal definition as possible and simple mathematics. I have heard rumors that you can compile documents online, and more specifically that Google has a free online compiler, but I have never been able to find any. Is there a way to compile documents online, so that I can write and compile documents even if I don't have a TeX distribution installed on my computer? The most common way to refer to non-immediate family? So in the image below there are two circles, how can I remove the internal vertices between them without messing up the outside shape. I'm working on a gun and this is just a simple way to illustrate the issue I'm dealing with. If I where to go in and delete the internal faces it would leave holes on the outside of the object, is there a fast way to get around this? What are the requirements for a (beta) site logo? So, for example, when I type man ls I see LS(1). But if I type man apachectl I see APACHECTL(8) and if I type man cd I end up with cd(n).  I'm wondering what the significance of the numbers in the parentheses are, if they have any. Is there a term for words that when reversed, form other words? I'm aware of what a palindrome is. What do you call words that, when reversed, form other words, such as ton (not) and part (trap)? Should methods in a Java interface be declared with or without a public access modifier? Should methods in a Java interface be declared with or without the public access modifier?  Technically it doesn't matter, of course. A class method that implements an interface is always public. But what is a better convention?  Java itself is not consistent in this. See for instance Collection vs. Comparable, or Future vs. ScriptEngine. linear transformation $T$ such that $TS = ST$ Let $V$ be a finite-dimensional vector space over $F$. Let $T:V \rightarrow V$ be a linear transformation such that $ST=TS$ for all linear transformations $S:V \rightarrow V$. Show that $T = cI_v$ for some $c \in F$. How do I pass have a Javascript script request a PHP page and pass data to it? How do I then have the PHP script pass data back to the Javascript script?  client.js:  data = {tohex: 4919, sum: [1, 3, 5]}; // how would this script pass data to server.php and access the response?   server.php:  $tohex = ... ; // How would this be set to data.tohex? $sum = ...; // How would this be set to data.sum? // How would this be sent to client.js? array(base_convert($tohex, 16), array_sum($sum)) How to get the file name from a full path using JavaScript? Is there a way that I can get the last value (based on the '\' symbol) from a full path?  Example:  C:\Documents and Settings\img\recycled log.jpg  With this case, I just want to get recycled log.jpg from the full path in JavaScript.