Catching NullPointerException is a really problematic thing to do since they can happen almost anywhere. It’s very easy to get one from a bug, catch it by accident and continue as if everything is normal, thus hiding a real problem. It’s so tricky to deal with so it’s best to avoid altogether. (For example, think … Read more
Yeah, it’s possible using $exists: db.things.find( { a : { $exists : false } } ); // return if a is missing When is true, $exists matches the documents that contain the field, including documents where the field value is null. If is false, the query returns only the documents that do not contain the … Read more
NULL values are sorted last in default ascending order. You don’t have to do anything extra. The issue applies to descending order, which is the perfect inverse and thus sorts NULL values on top. PostgreSQL 8.3 introduced NULLS LAST: ORDER BY somevalue DESC NULLS LAST For PostgreSQL 8.2 and older or other RDBMS without this … Read more
The question isn’t really “why is there a null value in JS” – there is a null value of some sort in most languages and it is generally considered very useful. The question is, “why is there an undefined value in JS”. Major places where it is used: when you declare var x; but don’t … Read more
If null were an Object, it would support the methods of java.lang.Object such as equals(). However, this is not the case – any method invocation on a null results in a NullPointerException. And this is what the Java Language Specification has to say on this topic: There is also a special null type, the type … Read more
With a simple generic function you can make this very easy. Just do this: return ConvertFromDBVal<string>(accountNumber); using the function: public static T ConvertFromDBVal<T>(object obj) { if (obj == null || obj == DBNull.Value) { return default(T); // returns the default value for the type } else { return (T)obj; } }
NULL is not a keyword. It’s an identifier defined in some standard headers. You can include #include <cstddef> To have it in scope, including some other basics, like std::size_t.
From C# 6 onwards, you can just use: MyEvent?.Invoke(); or: obj?.SomeMethod(); The ?. is the null-propagating operator, and will cause the .Invoke() to be short-circuited when the operand is null. The operand is only accessed once, so there is no risk of the “value changes between check and invoke” problem. === Prior to C# 6, … Read more
The reason for first one working: From MSDN: In string concatenation operations,the C# compiler treats a null string the same as an empty string, but it does not convert the value of the original null string. More information on the + binary operator: The binary + operator performs string concatenation when one or both operands … Read more
We have considered adding a new operation “?.” to the language that has the semantics you want. (And it has been added now; see below.) That is, you’d say cake?.frosting?.berries?.loader and the compiler would generate all the short-circuiting checks for you. It didn’t make the bar for C# 4. Perhaps for a hypothetical future version … Read more