Fix NullReferenceException for class type (#1182)

* Fix NullReferenceException for class type

* Add regression test

* Address PR comments: add comment where the special case can happen and simplify test case to one-liner

Author: bergmeister

Engine/Helper.cs

@@ -1093,8 +1093,8 @@ public string GetTypeFromMemberExpressionAst(MemberExpressionAst memberAst, Ast
 
                 if (details != null && classes != null)
                 {
-                    // Get the class that corresponds to the name of the type (if possible)
-                    psClass = classes.FirstOrDefault(item => String.Equals(item.Name, details.Type.FullName, StringComparison.OrdinalIgnoreCase));
+                    // Get the class that corresponds to the name of the type (if possible, the type is not available in the case of a static Singleton)
+                    psClass = classes.FirstOrDefault(item => String.Equals(item.Name, details.Type?.FullName, StringComparison.OrdinalIgnoreCase));
                 }
 
 #endif

Tests/Engine/InvokeScriptAnalyzer.tests.ps1

@@ -630,5 +630,12 @@ Describe "Test -EnableExit Switch" {
                 $warnings.RuleName | Should -Be 'TypeNotFound'
             }
         }
+
+        Describe "Handles static Singleton (issue 1182)" {
+            It "Does not throw or return diagnostic record" {
+                $scriptDefinition = 'class T { static [T]$i }; function foo { [CmdletBinding()] param () $script:T.WriteLog() }'
+                Invoke-ScriptAnalyzer -ScriptDefinition $scriptDefinition -ErrorAction Stop | Should -BeNullOrEmpty
+            }
+        }
     }
 }