Null Literals and Type Inference
Null literals are compatible with any type in the Entity SQL type system. However, for the type of a null literal to be inferred correctly, Entity SQL imposes certain constraints on where a null literal can be used.
Typed nulls can be used anywhere. Type inference is not required for typed nulls because the type is known. For example, you can construct a null of type Int16 with the following Entity SQL construct:
(cast(null as Int16))
Free-Floating Null Literals
Free-floating null literals can be used in the following contexts:
As an argument to a CAST or TREAT expression. This is the recommended way to produce a typed null expression.
As an argument to a method or a function. Standard overload rules apply.
As one of the arguments to an arithmetic expression such as +, -, or /. The other arguments cannot be null literals, otherwise type inference is not possible.
As any of the arguments to a logical expression (AND, OR, or NOT). All the arguments are known to be of type Boolean.
As the argument to an IS NULL or IS NOT NULL expression.
As one or more of the arguments to a LIKE expression. All arguments are expected to be strings.
As one or more of the arguments to a named-type constructor.
As one or more of the arguments to a multiset constructor. At least one argument to the multiset constructor must be an expression that is not a null literal.
As one or more of the THEN or ELSE expressions in a CASE expression. At least one of the THEN or ELSE expressions in the CASE expression must be an expression other than a null literal.
Free-floating null literals cannot be used in other scenarios. For example, they cannot be used as arguments to a row constructor.
ConceptsEntity SQL Overview