diff --git a/ICSharpCode.Decompiler/TypeSystem/IEntity.cs b/ICSharpCode.Decompiler/TypeSystem/IEntity.cs
index 92452c64a..c6c9c9f3a 100644
--- a/ICSharpCode.Decompiler/TypeSystem/IEntity.cs
+++ b/ICSharpCode.Decompiler/TypeSystem/IEntity.cs
@@ -58,8 +58,9 @@ namespace ICSharpCode.Decompiler.TypeSystem
 
 		/// <summary>
 		/// The module in which this entity is defined.
+		/// May return null, if the IEntity was not created from a module.
 		/// </summary>
-		IModule ParentModule { get; }
+		IModule? ParentModule { get; }
 
 		/// <summary>
 		/// Gets the attributes on this entity.
diff --git a/ILSpy/Commands/ScopeSearchToAssembly.cs b/ILSpy/Commands/ScopeSearchToAssembly.cs
index 89512a2c9..e2caeff7c 100644
--- a/ILSpy/Commands/ScopeSearchToAssembly.cs
+++ b/ILSpy/Commands/ScopeSearchToAssembly.cs
@@ -15,6 +15,8 @@
 // FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
+#nullable enable
+
 using System;
 
 using ICSharpCode.Decompiler.TypeSystem;
@@ -28,7 +30,8 @@ namespace ICSharpCode.ILSpy
 	{
 		public void Execute(TextViewContext context)
 		{
-			string asmName = GetAssembly(context);
+			// asmName cannot be null here, because Execute is only called if IsEnabled/IsVisible return true.
+			string asmName = GetAssembly(context)!;
 			string searchTerm = MainWindow.Instance.SearchPane.SearchTerm;
 			string[] args = NativeMethods.CommandLineToArgumentArray(searchTerm);
 			bool replaced = false;
@@ -62,10 +65,10 @@ namespace ICSharpCode.ILSpy
 			return GetAssembly(context) != null;
 		}
 
-		string GetAssembly(TextViewContext context)
+		string? GetAssembly(TextViewContext context)
 		{
 			if (context.Reference?.Reference is IEntity entity)
-				return entity.ParentModule.AssemblyName;
+				return entity.ParentModule?.AssemblyName;
 			if (context.SelectedTreeNodes?.Length != 1)
 				return null;
 			switch (context.SelectedTreeNodes[0])
@@ -73,7 +76,7 @@ namespace ICSharpCode.ILSpy
 				case AssemblyTreeNode tn:
 					return tn.LoadedAssembly.ShortName;
 				case IMemberTreeNode member:
-					return member.Member.ParentModule.AssemblyName;
+					return member.Member?.ParentModule?.AssemblyName;
 				default:
 					return null;
 			}
diff --git a/ILSpy/TreeNodes/IMemberTreeNode.cs b/ILSpy/TreeNodes/IMemberTreeNode.cs
index 2aa0d8619..81dbde36f 100644
--- a/ILSpy/TreeNodes/IMemberTreeNode.cs
+++ b/ILSpy/TreeNodes/IMemberTreeNode.cs
@@ -15,6 +15,7 @@
 // FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
 // OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 // DEALINGS IN THE SOFTWARE.
+#nullable enable
 
 using ICSharpCode.Decompiler.TypeSystem;
 
@@ -31,6 +32,6 @@ namespace ICSharpCode.ILSpy.TreeNodes
 		/// Returns the entity that is represented by this tree node.
 		/// May return null, if the member cannot be resolved.
 		/// </summary>
-		IEntity Member { get; }
+		IEntity? Member { get; }
 	}
 }