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System.NullReferenceException When checking if != null

由 馋奶兔 提交于 2019-12-10 18:03:19
问题 I'm using an ASHX handler, i want the handler to check if Session != null. if (context.Session["Username"] != null) And i get this error pointing this line: System.NullReferenceException: Object reference not set to an instance of an object. What's the problem? 回答1: if (context.Session["Username"] != null) Does your handler implement IRequiresSessionState? Otherwise Session might not be available. From MSDN: Specifies that the target HTTP handler requires read and write access to session

How to express 'null' value from web service as real null or empty string instead of 'null' string

由 我的未来我决定 提交于 2019-12-10 17:55:45
问题 In my application, I am using JSF and Java Web Services. When any of my web-service functions return a null value, it is always expressed as a "null" string. As a consequence, I cannot use EL expressions like #{empty object} to test for null values or empty strings. I'd like to ask if there's a way to configure such that Java Web Services will return null value as an empty string OR JSF/EL can understand "null" string as null value. 回答1: if you, using SOAP, you must remember that the SOAP

Is this a Pandas bug with notnull() or a fundamental misunderstanding on my part (probably misunderstanding)

由 ￣綄美尐妖づ 提交于 2019-12-10 17:06:28
问题 I have a pandas dataframe with two columns and default indexing. The first column is a string and the second is a date. The top date is NaN (though it should be NaT really). index somestr date 0 ON NaN 1 1C 2014-06-11 00:00:00 2 2C 2014-07-09 00:00:00 3 3C 2014-08-13 00:00:00 4 4C 2014-09-10 00:00:00 5 5C 2014-10-08 00:00:00 6 6C 2014-11-12 00:00:00 7 7C 2014-12-10 00:00:00 8 8C 2015-01-14 00:00:00 9 9C 2015-02-11 00:00:00 10 10C 2015-03-11 00:00:00 11 11C 2015-04-08 00:00:00 12 12C 2015-05

MySql query to get all combinations of two columns with NULL if there is no matching record

由 怎甘沉沦 提交于 2019-12-10 16:34:02
问题 I have a Table which has the records of the down time of a server. I have created a simplified version of this table at sqlfiddle. Please see here sqlfiddle The table has each record like Reason Month Down_Time A May 2 A May 5 B May 5 C July 15 A July 3 B June 6 A June 8 C June 2 I need to write a query to get all combinations of give Month and Reason with NULL if there is no matching record As an example : If I need to get the down time of the system in May, June and July due to Reason A,B

Swift 3 base64 decode return nil

由 只愿长相守 提交于 2019-12-10 16:33:38
问题 Despite all the methods I found on the internet. But it works through online translators. For example, a method I tried: if let decodedData = NSData(base64Encoded: parts[1] as String, options:NSData.Base64DecodingOptions(rawValue: 0)), let decodedString = NSString(data: decodedData as Data, encoding: String.Encoding.utf8.rawValue) { print(decodedString)//Here we are getting decoded string } 来源： https://stackoverflow.com/questions/40397136/swift-3-base64-decode-return-nil

How can I check for undefined method for nilClass before I error out?

由 蹲街弑〆低调 提交于 2019-12-10 16:23:24
问题 I am currently using the following: 20: <p>Status: <%= @contact.try(:status) unless @contact.nil? || @contac t.status.nil?%></p> However, I still get the following error: ActionView::TemplateError (undefined method `status' for nil:NilClass) on line # 20 of app/views/contacts/show.html.erb: Is there a better way to be checking? This seems to be a common problem -- it works fine in dev but I am not finding it in production.... 回答1: Use the Rails utility method try <%= @contact.try(:status) %>

how to remove emty elements from tcl list

由 北城余情 提交于 2019-12-10 16:19:15
问题 hi I have following list % set qprList {{{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} 12345 {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} 12345 {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} 12345 {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}} {{}}

Understanding NULL pointer in C

由 送分小仙女□ 提交于 2019-12-10 16:08:23
问题 I have found in some code NULL pointer is defined as follows - #define NULL ((char *)0) I found these code compiles fine. But I did not understand how this works. Can anyone please explain how 0 is casted to a char pointer? And is it valid to use it as a FILE pointer making null - FILE *fp = NULL; 回答1: The C library Macro NULL is the value of a null pointer constant.It may be defined as ((void*)0), 0 or 0L depending on the compiler vendor. Depending on compiler,declaration of NULL can be

Soap WSDL with Null

由 本秂侑毒 提交于 2019-12-10 15:56:48
问题 I need to specify a parameter in a function which is nullable. This doesn't work: <message name="SaveRequest"> <part name="serialNumber" nillable="true" type="xsd:int"/> </message> 回答1: <serialNumber xsi:nil="true" /> See w3.org XML Schema 来源： https://stackoverflow.com/questions/2540507/soap-wsdl-with-null

Optional使用方式

由 孤人 提交于 2019-12-10 15:30:55
Optional在jdk8中引入，已经有很长时间了，但是对于它的使用在平时的项目中最多只是拿它做下面这样的处理： XX e = Optional.ofNullable(xx.xx(x.x())) .orElseThrow(() -> new xxException("xxx")); 判断某个方法返回的值是否为null,如果是会抛出一个异常。 在Optional引入之前处理null都是使用if去判断，这样写起来有点繁琐，但是最主要的还是很容易忘记判断值是否为null。使用可能为null的值去执行程序会出现很多意想不到的结果，可能会抛出NPE，可能出现一些其他的问题。为了避免这些问题所以jdk8引入了Optional去处理，当然上面的例子只是很简单的使用，也可以说不是很正确的使用。 在哪用 在可能为空的成员变量的get方法上使用Optional返回 class Student { //name可能为null private String name; //id肯定不会为null private Integer id; public Student(String name) { this.name = name; } public Optional<String> getName() { return Optional.of(name); } public Integer getId(){
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