PS: Fix missing toString and accept test changes.

Author: MathiasVP

powershell/ql/lib/semmle/code/powershell/ast/internal/MemberExpr.qll

@@ -37,7 +37,12 @@ class MemberExpr extends Expr, TMemberExpr {
 
   predicate isStatic() { getRawAst(this).(Raw::MemberExpr).isStatic() }
 
-  final override string toString() { result = this.getMemberName() }
+  final override string toString() {
+    result = this.getMemberName()
+    or
+    not exists(this.getMemberName()) and
+    result = "..."
+  }
 
   predicate isExplicitWrite(Ast assignment) {
     explicitAssignment(getRawAst(this), getRawAst(assignment))

powershell/ql/test/library-tests/ast/Expressions/expressions.expected

@@ -5,7 +5,7 @@ cmdExpr
 | BinaryExpression.ps1:4:1:4:7 | [Stmt] result | BinaryExpression.ps1:4:1:4:7 | result |
 | ExpandableString.ps1:1:1:1:39 | [Stmt] Date: $([DateTime]::Now)\nName: $name | ExpandableString.ps1:1:1:1:39 | Date: $([DateTime]::Now)\nName: $name |
 | ExpandableString.ps1:1:23:1:37 | [Stmt] Now | ExpandableString.ps1:1:23:1:37 | Now |
-| MemberExpression.ps1:2:1:2:14 | (no string representation) | MemberExpression.ps1:2:1:2:14 | (no string representation) |
+| MemberExpression.ps1:2:1:2:14 | [Stmt] ... | MemberExpression.ps1:2:1:2:14 | ... |
 | SubExpression.ps1:1:1:1:23 | [Stmt] Call to AddDays | SubExpression.ps1:1:1:1:23 | Call to AddDays |
 | SubExpression.ps1:1:3:1:10 | [Stmt] Call to Get-Date | SubExpression.ps1:1:3:1:10 | Call to Get-Date |
 | SubExpression.ps1:2:1:2:21 | [Stmt] Call to AddDays | SubExpression.ps1:2:1:2:21 | Call to AddDays |
@@ -16,4 +16,4 @@ expandableString
 | ExpandableString.ps1:1:1:1:39 | Date: $([DateTime]::Now)\nName: $name | 1 | ExpandableString.ps1:1:21:1:38 | $(...) |
 memberExpr
 | ExpandableString.ps1:1:23:1:37 | Now | ExpandableString.ps1:1:23:1:32 | DateTime |
-| MemberExpression.ps1:2:1:2:14 | (no string representation) | MemberExpression.ps1:2:1:2:10 | DateTime |
+| MemberExpression.ps1:2:1:2:14 | ... | MemberExpression.ps1:2:1:2:10 | DateTime |