diff --git a/applications/test/HashSet/Test-hashSet.C b/applications/test/HashSet/Test-hashSet.C
index b4bdd07cab..3416abbe68 100644
--- a/applications/test/HashSet/Test-hashSet.C
+++ b/applications/test/HashSet/Test-hashSet.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011 OpenFOAM Foundation
-    Copyright (C) 2018-2021 OpenCFD Ltd.
+    Copyright (C) 2018-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -25,11 +25,11 @@ License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
 Description
+    Some simple HashSet tests
 
 \*---------------------------------------------------------------------------*/
 
 #include "hashedWordList.H"
-#include "nil.H"
 #include "HashOps.H"
 #include "HashSet.H"
 #include "Map.H"
@@ -123,7 +123,7 @@ int main(int argc, char *argv[])
         { "value3", 3 }
     });
 
-    HashTable<nil> tableB;
+    HashTable<Foam::zero> tableB;
     tableB.emplace("value4");
     tableB.emplace("value5");
     tableB.emplace("value6");
@@ -185,7 +185,7 @@ int main(int argc, char *argv[])
     Info<< wordHashSet(setA) << endl;
     Info<< "create from HashTable<T>: ";
     Info<< wordHashSet(tableA) << endl;
-    Info<< "create from HashTable<nil>: ";
+    Info<< "create from HashTable<zero>: ";
     Info<< wordHashSet(tableB) << endl;
 
     Info<< "create from Map<label>: ";
diff --git a/src/OpenFOAM/compat/nil.H b/src/OpenFOAM/compat/nil.H
deleted file mode 100644
index 6caa04dbc8..0000000000
--- a/src/OpenFOAM/compat/nil.H
+++ /dev/null
@@ -1,19 +0,0 @@
-// Compatibility include. Superseded (MAY-2017) by Foam::zero::null
-
-#ifndef FoamCompat_nil_H
-#define FoamCompat_nil_H
-
-#include "zero.H"
-
-namespace Foam
-{
-
-//- Superseded (MAY-2017) by Foam::zero::null
-//  \deprecated(2017-05) - use Foam::zero::null instead
-typedef zero::null nil;
-
-}
-
-#endif
-
-// ************************************************************************* //
diff --git a/src/OpenFOAM/containers/HashTables/HashSet/HashSet.H b/src/OpenFOAM/containers/HashTables/HashSet/HashSet.H
index 2288d57ead..cf659ecbaa 100644
--- a/src/OpenFOAM/containers/HashTables/HashSet/HashSet.H
+++ b/src/OpenFOAM/containers/HashTables/HashSet/HashSet.H
@@ -93,7 +93,7 @@ typedef HashSet<label, Hash<label>> labelHashSet;
 template<class Key, class Hash=Foam::Hash<Key>>
 class HashSet
 :
-    public HashTable<zero::null, Key, Hash>
+    public HashTable<Foam::zero, Key, Hash>
 {
     // Private Member Functions
 
@@ -113,7 +113,7 @@ public:
     typedef HashSet<Key, Hash> this_type;
 
     //- The template instance used for the parent HashTable
-    typedef HashTable<zero::null, Key, Hash> parent_type;
+    typedef HashTable<Foam::zero, Key, Hash> parent_type;
 
     //- An iterator, returning reference to the key
     using iterator = typename parent_type::key_iterator;
diff --git a/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H b/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H
index 7209f093a6..4becd58ebe 100644
--- a/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H
+++ b/src/OpenFOAM/containers/HashTables/HashTable/HashTable.H
@@ -132,7 +132,7 @@ public:
         //- with an additional linked-list entry for hash collisions
         typedef typename std::conditional
         <
-            std::is_same<zero::null, typename std::remove_cv<T>::type>::value,
+            std::is_same<Foam::zero, typename std::remove_cv<T>::type>::value,
             Detail::HashTableSingle<Key>,
             Detail::HashTablePair<Key, T>
         >::type node_type;
diff --git a/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H b/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H
index dadd621297..82b1b884b0 100644
--- a/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H
+++ b/src/OpenFOAM/containers/HashTables/HashTable/HashTableDetail.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -217,7 +217,7 @@ struct HashTableSingle
         typedef K key_type;
 
         //- Type of content (no content: placeholder)
-        typedef Foam::zero::null mapped_type;
+        typedef Foam::zero mapped_type;
 
         //- Content storage type to the entry
         typedef key_type value_type;
@@ -271,22 +271,22 @@ struct HashTableSingle
             return key_;
         }
 
-        //- Const access to the (dummy) mapped value
+        //- Const access to the (dummy) mapped value (for API only)
         const mapped_type& cval() const noexcept
         {
-            return Foam::zero::null::dummy;
+            return Foam::zero::dummy;
         }
 
-        //- Const access to the (dummy) mapped value
+        //- Const access to the (dummy) mapped value (for API only)
         const mapped_type& val() const noexcept
         {
-            return Foam::zero::null::dummy;
+            return Foam::zero::dummy;
         }
 
-        //- Non-const access to the (dummy) mapped value
+        //- Non-const access to the (dummy) mapped value (for API only)
         mapped_type& val() noexcept
         {
-            return Foam::zero::null::dummy;
+            return Foam::zero::dummy;
         }
 
 
diff --git a/src/OpenFOAM/meshes/primitiveShapes/cut/cut.H b/src/OpenFOAM/meshes/primitiveShapes/cut/cut.H
index f9a9ba6293..7b606c87ea 100644
--- a/src/OpenFOAM/meshes/primitiveShapes/cut/cut.H
+++ b/src/OpenFOAM/meshes/primitiveShapes/cut/cut.H
@@ -90,7 +90,7 @@ public:
 
 class noOp
 :
-    public uniformOp<zero::null>
+    public uniformOp<Foam::zero>
 {
 public:
 
@@ -106,9 +106,9 @@ public:
         noOp() = default;
 
         //- Construct from base
-        noOp(const uniformOp<zero::null>& op)
+        noOp(const uniformOp<Foam::zero>& op)
         :
-            uniformOp<zero::null>(op)
+            uniformOp<Foam::zero>(op)
         {}
 
 
@@ -135,7 +135,7 @@ public:
 
 class areaOp
 :
-    public uniformOp<zero::null>
+    public uniformOp<Foam::zero>
 {
 public:
 
@@ -151,9 +151,9 @@ public:
         areaOp() = default;
 
         //- Construct from base
-        areaOp(const uniformOp<zero::null>& op)
+        areaOp(const uniformOp<Foam::zero>& op)
         :
-            uniformOp<zero::null>(op)
+            uniformOp<Foam::zero>(op)
         {}
 
 
@@ -179,7 +179,7 @@ public:
 
 class volumeOp
 :
-    public uniformOp<zero::null>
+    public uniformOp<Foam::zero>
 {
 public:
 
@@ -195,9 +195,9 @@ public:
         volumeOp() = default;
 
         //- Construct from base
-        volumeOp(const uniformOp<zero::null>& op)
+        volumeOp(const uniformOp<Foam::zero>& op)
         :
-            uniformOp<zero::null>(op)
+            uniformOp<Foam::zero>(op)
         {}
 
 
@@ -310,7 +310,7 @@ public:
 template<unsigned N>
 class listOp
 :
-    public uniformOp<zero::null>
+    public uniformOp<Foam::zero>
 {
 public:
 
@@ -350,9 +350,9 @@ public:
         listOp() = default;
 
         //- Construct from base
-        listOp(const uniformOp<zero::null>& op)
+        listOp(const uniformOp<Foam::zero>& op)
         :
-            uniformOp<zero::null>(op)
+            uniformOp<Foam::zero>(op)
         {}
 
 
diff --git a/src/OpenFOAM/primitives/nullObject/nullObject.H b/src/OpenFOAM/primitives/nullObject/nullObject.H
index 70c96e1444..8d3793f50c 100644
--- a/src/OpenFOAM/primitives/nullObject/nullObject.H
+++ b/src/OpenFOAM/primitives/nullObject/nullObject.H
@@ -141,7 +141,7 @@ public:
 
         //- Swallow assignment (cf, std::ignore)
         template<class T>
-        const NullObject& operator=(const T&) const
+        const NullObject& operator=(const T&) const noexcept
         {
             return *this;
         }
diff --git a/src/OpenFOAM/primitives/traits/one.H b/src/OpenFOAM/primitives/traits/one.H
index eedd533011..d14d91fc88 100644
--- a/src/OpenFOAM/primitives/traits/one.H
+++ b/src/OpenFOAM/primitives/traits/one.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -65,9 +65,6 @@ public:
     //- The value type
     typedef one value_type;
 
-    // Forward Declarations
-    class minus;
-
     //- Default construct
     constexpr one() noexcept {}
 
@@ -101,53 +98,6 @@ public:
 };
 
 
-/*---------------------------------------------------------------------------*\
-                         Class one::minus Declaration
-\*---------------------------------------------------------------------------*/
-
-//- A class representing the concept of -1.
-//  \note this class must never be derived from Foam::one, since this could
-//  potentially mask its behaviour.
-class one::minus
-{
-public:
-
-    //- The value type
-    typedef minus value_type;
-
-    //- Default construct
-    constexpr minus() noexcept {}
-
-    //- Construct from Istream consumes no content.
-    explicit constexpr minus(Istream&) noexcept {}
-
-
-    //- Return -1 for label
-    constexpr operator label() const noexcept
-    {
-        return -1;
-    }
-
-    //- Return -1 for float
-    constexpr operator float() const noexcept
-    {
-        return -1;
-    }
-
-    //- Return -1 for double
-    constexpr operator double() const noexcept
-    {
-        return -1;
-    }
-
-    //- Component-wise or element-wise access returns minus one
-    one::minus operator[](const label) const noexcept
-    {
-        return one::minus{};
-    }
-};
-
-
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 //- Global one (1)
@@ -161,12 +111,6 @@ inline constexpr Istream& operator>>(Istream& is, one&) noexcept
     return is;
 }
 
-//- Read from Istream consumes no content.
-inline constexpr Istream& operator>>(Istream& is, one::minus&) noexcept
-{
-    return is;
-}
-
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/src/OpenFOAM/primitives/traits/zero.C b/src/OpenFOAM/primitives/traits/zero.C
index b7c98c4280..0d7e134580 100644
--- a/src/OpenFOAM/primitives/traits/zero.C
+++ b/src/OpenFOAM/primitives/traits/zero.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -32,7 +32,7 @@ Note
 
 // * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
 
-Foam::zero::null Foam::zero::null::dummy;
+Foam::zero Foam::zero::dummy;
 
 
 // ************************************************************************* //
diff --git a/src/OpenFOAM/primitives/traits/zero.H b/src/OpenFOAM/primitives/traits/zero.H
index 838aea7af9..bc0828165d 100644
--- a/src/OpenFOAM/primitives/traits/zero.H
+++ b/src/OpenFOAM/primitives/traits/zero.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2022 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -66,8 +66,8 @@ public:
     //- The value type
     typedef zero value_type;
 
-    // Forward Declarations
-    class null;
+    //- A static instance, when modifiable reference is required by an API
+    static zero dummy;
 
     //- Default construct
     constexpr zero() noexcept {}
@@ -105,30 +105,10 @@ public:
     {
         return zero{};
     }
-};
 
-
-/*---------------------------------------------------------------------------*\
-                         Class zero::null Declaration
-\*---------------------------------------------------------------------------*/
-
-//- A zero class with a null output adapter.
-class zero::null
-:
-    public zero
-{
-public:
-
-    typedef null value_type;
-
-    //- A static zero::null for dereferencing as a dummy element
-    static null dummy;
-
-    //- Default construct
-    constexpr null() noexcept {}
-
-    //- Construct from Istream consumes no content.
-    explicit constexpr null(Istream&) noexcept {}
+    // FUTURE?: Swallow assignment (as per std::ignore)
+    // template<class T>
+    // constexpr const zero& operator=(const T&) const { return *this; }
 };
 
 
@@ -145,12 +125,6 @@ inline constexpr Istream& operator>>(Istream& is, zero&) noexcept
     return is;
 }
 
-//- Write to Ostream emits no content
-inline constexpr Ostream& operator<<(Ostream& os, const zero::null&) noexcept
-{
-    return os;
-}
-
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
diff --git a/src/meshTools/edgeMesh/extendedEdgeMesh/extendedEdgeMesh.C b/src/meshTools/edgeMesh/extendedEdgeMesh/extendedEdgeMesh.C
index 4a224af40d..f65587e9f7 100644
--- a/src/meshTools/edgeMesh/extendedEdgeMesh/extendedEdgeMesh.C
+++ b/src/meshTools/edgeMesh/extendedEdgeMesh/extendedEdgeMesh.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2015-2022 OpenCFD Ltd.
+    Copyright (C) 2015-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -400,7 +400,7 @@ Foam::extendedEdgeMesh::extendedEdgeMesh()
 {}
 
 
-Foam::extendedEdgeMesh::extendedEdgeMesh(class one::minus)
+Foam::extendedEdgeMesh::extendedEdgeMesh(std::nullptr_t)
 :
     edgeMesh(),
     concaveStart_(-1),
@@ -486,7 +486,7 @@ Foam::extendedEdgeMesh::extendedEdgeMesh
     const boolList& surfBaffleRegions
 )
 :
-    extendedEdgeMesh(one::minus{})
+    extendedEdgeMesh(nullptr)
 {
     // Extract and reorder the data from surfaceFeatures
     const triSurface& surf = sFeat.surface();
@@ -549,7 +549,7 @@ Foam::extendedEdgeMesh::extendedEdgeMesh
     const labelUList& featurePoints
 )
 :
-    extendedEdgeMesh(one::minus{})
+    extendedEdgeMesh(nullptr)
 {
     sortPointsAndEdges
     (
diff --git a/src/meshTools/edgeMesh/extendedEdgeMesh/extendedEdgeMesh.H b/src/meshTools/edgeMesh/extendedEdgeMesh/extendedEdgeMesh.H
index 254b48969b..02ec08b26e 100644
--- a/src/meshTools/edgeMesh/extendedEdgeMesh/extendedEdgeMesh.H
+++ b/src/meshTools/edgeMesh/extendedEdgeMesh/extendedEdgeMesh.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2015-2020 OpenCFD Ltd.
+    Copyright (C) 2015-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -205,7 +205,7 @@ protected:
     // Protected Constructors
 
         //- Construct null, initializing start indices with -1
-        explicit extendedEdgeMesh(class one::minus);
+        explicit extendedEdgeMesh(std::nullptr_t);
 
 
     // Protected Member Functions