Item 31: §11.2.2 Add nullable conversions to pattern compatibility

Add "a nullable value type conversion" to the list of conversions that make type `E` pattern-compatible with `T`.

Author: BillWagner

standard/patterns.md

@@ -90,7 +90,7 @@ The runtime type of the value is tested against the *type* in the pattern using
 
 Given a pattern input value ([§11.1](patterns.md#111-general)) *e*, if the *simple_designation* is *discard_designation*, it denotes a discard ([§9.2.9.2](variables.md#9292-discards)), and the value of *e* is not bound to anything. (Although a declared variable with the name `_` may be in scope at that point, that named variable is not seen in this context.) Otherwise, if the *simple_designation* is *single_variable_designation*, a local variable ([§9.2.9](variables.md#929-local-variables)) of the given type named by the given identifier is introduced. That local variable is assigned the value of the pattern input value when the pattern *matches* the value.  
 
-Certain combinations of static type of the pattern input value and the given type are considered incompatible and result in a compile-time error. A value of static type `E` is said to be ***pattern compatible*** with the type `T` if there exists an identity conversion, an implicit or explicit reference conversion, a boxing conversion, or an unboxing conversion from `E` to `T`, or if either `E` or `T` is an open type ([§8.4.3](types.md#843-open-and-closed-types)). A declaration pattern naming a type `T` is *applicable to* every type `E` for which `E` is pattern compatible with `T`.
+Certain combinations of static type of the pattern input value and the given type are considered incompatible and result in a compile-time error. A value of static type `E` is said to be ***pattern compatible*** with the type `T` if there exists an identity conversion, an implicit or explicit reference conversion, a boxing conversion, an unboxing conversion, or an implicit or explicit nullable value type conversion from `E` to `T`, or if either `E` or `T` is an open type ([§8.4.3](types.md#843-open-and-closed-types)). A declaration pattern naming a type `T` is *applicable to* every type `E` for which `E` is pattern compatible with `T`.
 
 > *Note*: The support for open types can be most useful when checking types that may be either struct or class types, and boxing is to be avoided. *end note*
 <!-- markdownlint-disable MD028 -->