I don't understand the error
What is a NullPointerException, and how do I fix it?
I just failed these   in First Post, I read the question and thought it seemed reasonable but the user was deleted so to be on the safe side I clicked add comment and I failed the audit.  I'm not sure why adding a comment would be considered a negative action, is the correct option to click No Action Needed or edit?  What was I supposed to do in this situation?  Adding a comment should not be a review audit fail. Why are Flash applications so sluggish/crashy? I've noticed that Flash applications tend to be more sluggish under Ubuntu than they do under Windows on the same machine. This is particularly noticeable when watching HD video or playing graphics/physics-heavy games. Are there any ways of improving the performance of Flash under Ubuntu, or is this just an issue with the Linux version that I will have to live with?  Currently I'm just cutting down on the number of tabs open, blocking flash ads, and closing other programs, but I'm looking for ways to affect Flash itself.  Other things I have already been doing include using Youtube's HTML5 feature and playing videos straight from /tmp in VLC. I was wondering if there was some way of streamlining Flash itself though. Perhaps not.  More Specific Question: Is there anything I can do in mms.cfg to boost performance? I'm new to the world of Apple, I bought a new Macbook Pro, mid-2020, Intel i7, 16GB RAM. I'm a developer, I run apps like VS Code, Sublime Text, Slack, Chrome (Multiple Windows), I play videos/songs in the background. I have been keeping a track of the energy consumption on my Mac, and it only runs for 4 hours. I have reset my SMC after I upgraded to Big Sur. Is 4 hours normal? or should I go to the service center? Update on 3 Feb 2021: I submitted my Mac to the Apple service center they said they conducted a few tests and the conclusion was that the battery is fine (I don't know what type of test they did). So I guess I'll be using it on AC Update on 12 Feb 2021: Took it to the service center, they didn't find any issues so I started using Safari for work and my battery has improved by 1 hour on Average. Is there a standard naming convention for XML elements? Is there any standard, de facto or otherwise, for XML documents? For example which is the "best" way to write a tag?  &lt;MyTag /&gt; &lt;myTag /&gt; &lt;mytag /&gt; &lt;my-tag /&gt; &lt;my_tag /&gt;   Likewise if I have an enumerated value for an attribute which is better  &lt;myTag attribute="value one"/&gt; &lt;myTag attribute="ValueOne"/&gt; &lt;myTag attribute="value-one"/&gt; The tag  and meta-tag  syntax generate much nicer looking results than merely surrounding your tag with [square brackets].    However, they only work when you're talking about the site you're on.  On Area51, in Chat, and on Meta sites, this is frequently not the case, leading to attempts at syntax like [[tag:failure]](https://superuser.com/questions/tagged/failure), which produces:    Hmm, must be some subtle syntax thing:   : [tag:failure](https://superuser.com/questions/tagged/failure) []: [[tag:failure](https://superuser.com/questions/tagged/failure)] : [tag:[failure]((https://superuser.com/questions/tagged/failure))] : &lt;a href="https://superuser.com/questions/tagged/failure"&gt;[tag:failure]&lt;/a&gt; : [tag:failure][1] \n\n [1]: https://superuser.com/questions/tagged/failure : [more text is a [tag:failure] too](https://superuser.com/questions/tagged/failure)   I give up!  How can I create a link to a tag on another site with tag markdown? A real solution to ambiguous tags Introduction Even within a site's relatively focused range of topics (it's unlikely anybody on SO will think  refers to the solar system's star), some tags are inherently ambiguous. There are currently two unsatisfying options:  Declare that the tag is only to be used for one of the possible meanings, write a tag wiki explaining it, and link from there to the newly created tags for the other meanings, and keep cleaning up the tag whenever someone ignores the tag wiki popup explaining the tag. Use alternative tags for all meanings (e.g. cd-command and compact-disk, instead of cd), and keep removing the undesired tag whenever it pops up again. And it will. The  is not deterring users from creating unnecessary or redundant tags.  Blacklisting tags is a complicated ritual occurring once in a blue moon, at most, and involves a dragon, a team member, and sacrifices to be burnt. It also makes those other, unambiguous tags not easier to discover, if it were applied to ambiguous tags. I don't consider this to be a viable option in this case. Proposal Here's the proposed : Just like a tag can be declared a synonym of another tag, basically changing all references to the synonym to references to that other, canonical tag, it should be possible to make it a disambiguation tag (or ambiguous tag) for multiple other tags. It's a logical progression from &quot;You entered a term with the same meaning as this other term&quot; to &quot;You entered a term with the same meaning as one of these other terms, please choose the correct meaning&quot;. Use of the tag should force the user to choose one of the alternatives presented:  &quot;, did you mean  or ?&quot; &quot;, did you mean , , or ?&quot; &quot;You entered 'vm', did you mean  or ?&quot; &quot;You entered 'sas', did you mean  or ?&quot; &quot;You entered 'kvm', did you mean  or ?&quot; &quot;You entered 'mono', did you mean  or ?&quot; &quot;You entered 'dsl', did you mean  or ?&quot;  Not all of these examples might be good (I'm not sure e.g. about the first two SO examples), but that's not really the point here anyway — they should just convey how this could be used. Note how some of these tags would probably never be used if users had to type them, and yet everything shorter is ambiguous. This could probably be mostly solved by extending the synonym/tag wiki excerpt dropdowns shown when a user enters the tags, proposing the alternatives for an ambiguous tag entered by the user (like a synonym suggestion, but with multiple options). If ignored, the user could still be shown an error message like with blacklisted tags, but by designing the selection dialog well, it should be possible to prevent that in most cases.  Related topics   This topic is related, but the user seems to have accepted the inclusion of tag wiki excerpts in the tag suggestions drop-down as sufficient.   This requires extensive discussion and team involvement (i.e. the status quo)   This topic has no real solution, except manual retagging. Why do objects sometimes fall on their own? I have observed sometimes that when I keep some objects precariously balanced, for e.g. some objects in a cupboard, they seem quite stable at the time when I place them there but after a certain period, maybe even 8 - 12 hours suddenly you hear a noise and you can see that they have fallen for what seems like no apparent reason. What can be the reason for this? obviously, I am looking for a physics explanation and not a supernatural one. Activate physics by keyframe I'd like to have a group of debris fall from a ceiling onto the floor, but not have them drop all at the same time. Is there a way to set a keyframe that dictates when the object enters the simulation? For example, object 1 starts falling on frame 0, object 2 on frame 5, object 3 on frame 24, etc. What does the complex electric field show? We have a complex electric field. Is there any definition for absolute and imaginary part of a complex electric field? What do they stand for? I'm looking for a Drupal Commerce Shipping in-cart estimate Operator font in beamer/metropolis When using the metropolis theme for beamer, I get text and math in Fira Sans, except for math operators. I compile the following MWE using LuaTeX.  \documentclass{beamer}  \usetheme{metropolis}  \begin{document}    \begin{frame}     Ordinary text.     \[ a^2 + b^2 = \sin^2(x) - \mathsf{y} + \mathrm{z}  \]   \end{frame}  \end{document}   The outcome for me is that a, b, 2 and x are set in Fira Sans Light Italic, and y is set in Fira Sans Light, but sin is set in the sans font of (I guess) Latin Modern. (The z is also in Latin Modern, but this is expected behaviour from beamer.)  Unsurprisingly, I get the same result if I replace \usetheme{metropolis} with  \usepackage[no-math]{fontspec} \setsansfont[ItalicFont={Fira Sans Light Italic},   BoldFont={Fira Sans},   BoldItalicFont={Fira Sans Italic}]%   {Fira Sans Light}   I guess that this is to do with beamer's patching parts of the math fonts to match the text font (see ). However, I don't understand the font system well enough to modify this.  There was , but I've no idea how to apply that answer when using fontspec, or if this is even possible.  Is there a way to change the operator font to match the upright/sans math font (i.e., Fira Sans Light)? When I add LIMIT 1 to a MySQL query, does it stop the search after it finds 1 result (thus making it faster) or does it still fetch all of the results and truncate at the end? Geometric interpretation of $\frac {\partial^2} {\partial x \partial y} f(x,y)$ Is there an irrational number $a$ such that $a^a$ is rational? It can be proved that there are two irrational numbers $a$ and $b$ such that $a^b$ is rational (see ) and that for each irrational number $c$ there exists another irrational number $d$ such that $c^d$ is rational (see ).  My question is: Is there an irrational number $a$ such that $a^a$ is rational (and how could you prove that)? How do I create silhouettes in a studio environment? The trick to creating silhouettes in the field, as far as I know, is to use spot-metering and to expose for the background. However, this is a bit more difficult in a studio environment. What is the key to creating "artificial" silhouettes?  One solution that I'm considering is placing a bright flash directly behind the subject - would that work? zsh scripting - How do I NOT match a pattern in filename generation? I'm currently trying to loop through a set of directories, but only the ones I care about.   $ ls -d */ cfdpost_statefiles/     p050L0260/  p050L0510/  p060L0390/  p070L0260/  p070L0510/  p092L0390/  p097L0260/  p110L0390/  p131L0325/  p150L0510/  profiles/ ERCOFTAC_TestSettings/  p050L0390/  p060L0260/  p060L0510/  p070L0390/  p084L0510/  p094L0325/  p100L0510/  p125L0510/  p136L0260/  p162L0260/  settings/   I want to match all the p###* directories except for the ones beginning with p125 and p150.  If I just do patterns with a pipe, I get:  $ for dir in ./p(125|150)*(/); echo $dir ./p125L0510 ./p150L0510   However, if I try and use the ^ like it shows :  $ for dir in ./p^(125|150)*(/); echo $dir zsh: no matches found: ./p^(125|150)*(/)   Any ideas how to proceed? How rare are magic items and how many should I be handing out? How to know current name of the database in Django? Best way to parse command line arguments in C#? When building console applications that take parameters, you can use the arguments passed to Main(string[] args).   In the past I've simply indexed/looped that array and done a few regular expressions to extract the values. However, when the commands get more complicated, the parsing can get pretty ugly.    So I'm interested in:   Libraries that you use Patterns that you use   Assume the commands always adhere to common standards such as . Let $r$ be a relation on $A \times A$ such that $(a,b) r (c,d) \iff ad = bc.$ How can I show that this relation is transitive, ie. $(a, b)r(c,d)$ and $(c,d)r(e, f) \implies (a,b)r(e,f)$?  I tried to say that $(a,b) r (c,d)$ means that $c=ka$ and $d=kb,$ $k$ a coefficient, such that $ad = bc \iff akb = bka,$ and going on from there, but I'm not sure this is valid for all values of $a, b, c,$ and $d$. How can I show the transitivity of the relation?