Merge pull request #16 from stephentoub/fix_nullempty_array

Update spec'd behavior of fixed with null/empty array

spec/unsafe-code.md

@@ -705,7 +705,7 @@ Each *fixed_pointer_declarator* declares a local variable of the given *pointer_
 A *fixed_pointer_initializer* can be one of the following:
 
 *  The token "`&`" followed by a *variable_reference* ([Precise rules for determining definite assignment](variables.md#precise-rules-for-determining-definite-assignment)) to a moveable variable ([Fixed and moveable variables](unsafe-code.md#fixed-and-moveable-variables)) of an unmanaged type `T`, provided the type `T*` is implicitly convertible to the pointer type given in the `fixed` statement. In this case, the initializer computes the address of the given variable, and the variable is guaranteed to remain at a fixed address for the duration of the `fixed` statement.
-*  An expression of an *array_type* with elements of an unmanaged type `T`, provided the type `T*` is implicitly convertible to the pointer type given in the `fixed` statement. In this case, the initializer computes the address of the first element in the array, and the entire array is guaranteed to remain at a fixed address for the duration of the `fixed` statement. The behavior of the `fixed` statement is implementation-defined if the array expression is null or if the array has zero elements.
+*  An expression of an *array_type* with elements of an unmanaged type `T`, provided the type `T*` is implicitly convertible to the pointer type given in the `fixed` statement. In this case, the initializer computes the address of the first element in the array, and the entire array is guaranteed to remain at a fixed address for the duration of the `fixed` statement. If the array expression is null or if the array has zero elements, the initializer computes an address equal to zero.
 *  An expression of type `string`, provided the type `char*` is implicitly convertible to the pointer type given in the `fixed` statement. In this case, the initializer computes the address of the first character in the string, and the entire string is guaranteed to remain at a fixed address for the duration of the `fixed` statement. The behavior of the `fixed` statement is implementation-defined if the string expression is null.
 *  A *simple_name* or *member_access* that references a fixed size buffer member of a moveable variable, provided the type of the fixed size buffer member is implicitly convertible to the pointer type given in the `fixed` statement. In this case, the initializer computes a pointer to the first element of the fixed size buffer ([Fixed size buffers in expressions](unsafe-code.md#fixed-size-buffers-in-expressions)), and the fixed size buffer is guaranteed to remain at a fixed address for the duration of the `fixed` statement.