Workaround issue with Box.unbox causing segfault

Using Box.unbox on a nil value with a union type causes:

Invalid memory access (signal 11) at address 0x8

Related Crystal issue: https://github.com/crystal-lang/crystal/issues/11839
Fixes: https://gitlab.com/arctic-fox/spectator/-/issues/76

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+### Fixed
+- Workaround nilable type issue with memoized value. [#76](https://gitlab.com/arctic-fox/spectator/-/issues/76)
+
 ## [0.11.0] - 2022-07-14
 ### Changed
 - Overhauled mock and double system. [#63](https://gitlab.com/arctic-fox/spectator/-/issues/63)

spec/issues/gitlab_issue_76_spec.cr

@@ -0,0 +1,6 @@
+require "../spec_helper"
+
+Spectator.describe "GitLab Issue #76" do
+  let(:value) { nil.as(Int32?) }
+  specify { expect(value).to be_nil }
+end

src/spectator/wrapper.cr

@@ -19,7 +19,12 @@ module Spectator
     # Retrieves the previously wrapped value.
     # The *type* of the wrapped value must match otherwise an error will be raised.
     def get(type : T.class) : T forall T
-      Box(T).unbox(@pointer)
+      {% begin %}
+        {% if T.nilable? %}
+          @pointer.null? ? nil :
+        {% end %}
+        Box(T).unbox(@pointer)
+      {% end %}
     end
 
     # Retrieves the previously wrapped value.
@@ -34,7 +39,12 @@ module Spectator
     # type = wrapper.get { Int32 } # Returns Int32
     # ```
     def get(& : -> T) : T forall T
-      Box(T).unbox(@pointer)
+      {% begin %}
+        {% if T.nilable? %}
+          @pointer.null? ? nil :
+        {% end %}
+        Box(T).unbox(@pointer)
+      {% end %}
     end
   end
 end