Negation of operators on nullable values is not allowed for correct decompilation

ICSharpCode.Decompiler/Ast/AstMethodBodyBuilder.cs

@@ -747,6 +747,8 @@ namespace ICSharpCode.Decompiler.Ast
 					}
 				case ILCode.InitializedObject:
 					return new InitializedObjectExpression();
+				case ILCode.Wrap:
+					return new ParenthesizedExpression(arg1);
 				case ILCode.AddressOf:
 					return MakeRef(arg1);
 				default:

ICSharpCode.Decompiler/ILAst/ILCodes.cs

@@ -258,6 +258,11 @@ namespace ICSharpCode.Decompiler.ILAst
 		LogicOr,
 		NullCoalescing,
 		InitArray, // Array Initializer
+
+		/// <summary>
+		/// Defines a barrier between the parent opcode and argument opcode that prevents combining them
+		/// </summary>
+		Wrap,
 		
 		// new Class { Prop = 1, Collection = { { 2, 3 }, {4, 5} }}
 		// is represented as:

ICSharpCode.Decompiler/ILAst/NullableOperators.cs

@@ -325,10 +325,11 @@ namespace ICSharpCode.Decompiler.ILAst
 					var pm = new PatternMatcher();
 					if (!pm.Match(ps[i], expr)) continue;
 					var n = pm.BuildNew(OperatorVariableAB, expr);
-					expr.Code = n.Code;
-					expr.Operand = n.Operand;
-					expr.Arguments = n.Arguments;
-					expr.ILRanges = n.ILRanges;
+					expr.Code = ILCode.Wrap;
+					expr.Operand = null;
+					expr.Arguments.Clear();
+					expr.Arguments.Add(n);
+					expr.ILRanges.Clear();
 					expr.InferredType = n.InferredType;
 					return true;
 				}

ICSharpCode.Decompiler/ILAst/TypeAnalysis.cs

@@ -749,6 +749,7 @@ namespace ICSharpCode.Decompiler.ILAst
 					#endregion
 				case ILCode.Pop:
 					return null;
+				case ILCode.Wrap:
 				case ILCode.Dup:
 					return InferTypeForExpression(expr.Arguments.Single(), expectedType);
 				default: