From ba3aa8fab590ba22c163ffe18c8dcb8787959043 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Wed, 4 May 2022 16:21:06 -0400
Subject: [PATCH] remove NULL option for reset_timestep

---
 doc/src/reset_timestep.rst                 | 6 ++----
 src/update.cpp                             | 5 ++---
 unittest/commands/test_simple_commands.cpp | 7 -------
 3 files changed, 4 insertions(+), 14 deletions(-)

diff --git a/doc/src/reset_timestep.rst b/doc/src/reset_timestep.rst
index e6255e2167..fdaec81fa9 100644
--- a/doc/src/reset_timestep.rst
+++ b/doc/src/reset_timestep.rst
@@ -10,7 +10,7 @@ Syntax
 
    reset_timestep N keyword values ...
 
-* N = timestep number (may be NULL)
+* N = timestep number
 * zero or more keyword/value pairs may be appended
 * keyword = *time*
 
@@ -27,7 +27,6 @@ Examples
    reset_timestep 0
    reset_timestep 4000000
    reset_timestep 1000 time 100.0
-   reset_timestep NULL time 200.0
 
 Description
 """""""""""
@@ -40,8 +39,7 @@ simulation run or minimization advanced the timestep.
 The optional *time* keyword allows to also set the accumulated
 simulation time.  This is usually the number of timesteps times
 the size of the timestep, but when using variable size timesteps
-with :doc:`fix dt/reset <fix_dt_reset>` it can differ.  With
-NULL as the timestep number, only the accumulated time is reset.
+with :doc:`fix dt/reset <fix_dt_reset>` it can differ.
 
 The :doc:`read_data <read_data>` and :doc:`create_box <create_box>`
 commands set the timestep to 0; the :doc:`read_restart <read_restart>`
diff --git a/src/update.cpp b/src/update.cpp
index e9a533df58..8b8dd3d49b 100644
--- a/src/update.cpp
+++ b/src/update.cpp
@@ -459,11 +459,10 @@ void Update::reset_timestep(int narg, char **arg)
 {
   if (narg < 1) utils::missing_cmd_args(FLERR, "reset_timestep", error);
 
-  if (!utils::strmatch(arg[0], "^NULL$"))
-    reset_timestep(utils::bnumeric(FLERR, arg[0], false, lmp), true);
+  reset_timestep(utils::bnumeric(FLERR, arg[0], false, lmp), true);
 
   if (narg > 1) {
-    if (utils::strmatch(arg[1], "^time$")) {
+    if (strcmp(arg[1], "time") == 0) {
       if (narg < 3) utils::missing_cmd_args(FLERR, "reset_timestep time", error);
       atimestep = ntimestep;
       atime = utils::numeric(FLERR, arg[2], false, lmp);
diff --git a/unittest/commands/test_simple_commands.cpp b/unittest/commands/test_simple_commands.cpp
index 1d8d38fb27..ddedae4e9a 100644
--- a/unittest/commands/test_simple_commands.cpp
+++ b/unittest/commands/test_simple_commands.cpp
@@ -241,13 +241,6 @@ TEST_F(SimpleCommandsTest, ResetTimestep)
     ASSERT_EQ(lmp->update->atimestep, 0);
     ASSERT_DOUBLE_EQ(lmp->update->atime, 0.0);
 
-    BEGIN_HIDE_OUTPUT();
-    command("reset_timestep NULL time 10.0");
-    END_HIDE_OUTPUT();
-    ASSERT_EQ(lmp->update->ntimestep, 0);
-    ASSERT_EQ(lmp->update->atimestep, 0);
-    ASSERT_DOUBLE_EQ(lmp->update->atime, 10.0);
-
     BEGIN_HIDE_OUTPUT();
     command("reset_timestep 10 time 100.0");
     END_HIDE_OUTPUT();