diff --git a/docs/src/users_guide/time_evolution/solution.md b/docs/src/users_guide/time_evolution/solution.md
index efaea742f..8889f5604 100644
--- a/docs/src/users_guide/time_evolution/solution.md
+++ b/docs/src/users_guide/time_evolution/solution.md
@@ -84,7 +84,7 @@ State vectors, or density matrices, are accessed in a similar manner:
 sol.states
 ```
 
-Here, the solution contains only one (final) state. Because the `states` will be saved depend on the keyword argument `saveat` in `kwargs`. If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). One can also specify `e_ops` and `saveat` separately.
+Here, the solution contains only one (final) state. Because the `states` will be saved depend on the keyword argument `saveat` in `kwargs`. If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). One can also specify `e_ops` and `saveat` separately.
 
 Some other solvers can have other output.
 
diff --git a/src/time_evolution/mcsolve.jl b/src/time_evolution/mcsolve.jl
index 4eaf30ad7..58913233f 100644
--- a/src/time_evolution/mcsolve.jl
+++ b/src/time_evolution/mcsolve.jl
@@ -176,7 +176,7 @@ If the environmental measurements register a quantum jump, the wave function und
 # Notes
 
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-6` and `abstol=1e-8`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (ODE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/ode_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)
@@ -216,11 +216,11 @@ function mcsolveProblem(
         e_ops2 = MT1[]
     else
         expvals = Array{ComplexF64}(undef, length(e_ops), length(t_l))
-        is_empty_e_ops_mc = false
         e_ops2 = get_data.(e_ops)
+        is_empty_e_ops_mc = isempty(e_ops)
     end
 
-    saveat = e_ops isa Nothing ? t_l : [t_l[end]]
+    saveat = is_empty_e_ops_mc ? t_l : [t_l[end]]
     # We disable the progress bar of the sesolveProblem because we use a global progress bar for all the trajectories
     default_values = (DEFAULT_ODE_SOLVER_OPTIONS..., saveat = saveat, progress_bar = Val(false))
     kwargs2 = merge(default_values, kwargs)
@@ -373,7 +373,7 @@ If the environmental measurements register a quantum jump, the wave function und
 # Notes
 
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-6` and `abstol=1e-8`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (ODE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/ode_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)
@@ -514,7 +514,7 @@ If the environmental measurements register a quantum jump, the wave function und
 
 - `ensemble_method` can be one of `EnsembleThreads()`, `EnsembleSerial()`, `EnsembleDistributed()`
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-6` and `abstol=1e-8`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (ODE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/ode_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)
diff --git a/src/time_evolution/mesolve.jl b/src/time_evolution/mesolve.jl
index 3188e3b45..994bdb08c 100644
--- a/src/time_evolution/mesolve.jl
+++ b/src/time_evolution/mesolve.jl
@@ -88,7 +88,7 @@ where
 # Notes
 
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-6` and `abstol=1e-8`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (ODE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/ode_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)
@@ -154,7 +154,7 @@ function mesolveProblem(
         params...,
     )
 
-    saveat = e_ops isa Nothing ? t_l : [t_l[end]]
+    saveat = is_empty_e_ops ? t_l : [t_l[end]]
     default_values = (DEFAULT_ODE_SOLVER_OPTIONS..., saveat = saveat)
     kwargs2 = merge(default_values, kwargs)
     kwargs3 = _generate_mesolve_kwargs(e_ops, makeVal(progress_bar), t_l, kwargs2)
@@ -205,7 +205,7 @@ where
 # Notes
 
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-6` and `abstol=1e-8`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (ODE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/ode_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)
diff --git a/src/time_evolution/sesolve.jl b/src/time_evolution/sesolve.jl
index b30ed2cb2..f2699776e 100644
--- a/src/time_evolution/sesolve.jl
+++ b/src/time_evolution/sesolve.jl
@@ -75,7 +75,7 @@ Generates the ODEProblem for the Schrödinger time evolution of a quantum system
 # Notes
 
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-6` and `abstol=1e-8`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (ODE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/ode_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)
@@ -131,7 +131,7 @@ function sesolveProblem(
         params...,
     )
 
-    saveat = e_ops isa Nothing ? t_l : [t_l[end]]
+    saveat = is_empty_e_ops ? t_l : [t_l[end]]
     default_values = (DEFAULT_ODE_SOLVER_OPTIONS..., saveat = saveat)
     kwargs2 = merge(default_values, kwargs)
     kwargs3 = _generate_sesolve_kwargs(e_ops, makeVal(progress_bar), t_l, kwargs2)
@@ -174,7 +174,7 @@ Time evolution of a closed quantum system using the Schrödinger equation:
 # Notes
 
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-6` and `abstol=1e-8`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (ODE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/ode_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)
diff --git a/src/time_evolution/ssesolve.jl b/src/time_evolution/ssesolve.jl
index fae961178..79bb5286c 100644
--- a/src/time_evolution/ssesolve.jl
+++ b/src/time_evolution/ssesolve.jl
@@ -127,7 +127,7 @@ Above, `C_n` is the `n`-th collapse operator and  `dW_j(t)` is the real Wiener i
 # Notes
 
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-2` and `abstol=1e-2`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (SDE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/sde_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)
@@ -194,7 +194,7 @@ function ssesolveProblem(
         params...,
     )
 
-    saveat = e_ops isa Nothing ? t_l : [t_l[end]]
+    saveat = is_empty_e_ops ? t_l : [t_l[end]]
     default_values = (DEFAULT_SDE_SOLVER_OPTIONS..., saveat = saveat)
     kwargs2 = merge(default_values, kwargs)
     kwargs3 = _generate_sesolve_kwargs(e_ops, Val(false), t_l, kwargs2)
@@ -271,7 +271,7 @@ Above, `C_n` is the `n`-th collapse operator and  `dW_j(t)` is the real Wiener i
 # Notes
 
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-2` and `abstol=1e-2`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (SDE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/sde_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)
@@ -385,7 +385,7 @@ Above, `C_n` is the `n`-th collapse operator and  `dW_j(t)` is the real Wiener i
 
 - `ensemble_method` can be one of `EnsembleThreads()`, `EnsembleSerial()`, `EnsembleDistributed()`
 - The states will be saved depend on the keyword argument `saveat` in `kwargs`.
-- If `e_ops` is specified, the default value of `saveat=[tlist[end]]` (only save the final state), otherwise, `saveat=tlist` (saving the states corresponding to `tlist`). You can also specify `e_ops` and `saveat` separately.
+- If `e_ops` is empty, the default value of `saveat=tlist` (saving the states corresponding to `tlist`), otherwise, `saveat=[tlist[end]]` (only save the final state). You can also specify `e_ops` and `saveat` separately.
 - The default tolerances in `kwargs` are given as `reltol=1e-2` and `abstol=1e-2`.
 - For more details about `alg` please refer to [`DifferentialEquations.jl` (SDE Solvers)](https://docs.sciml.ai/DiffEqDocs/stable/solvers/sde_solve/)
 - For more details about `kwargs` please refer to [`DifferentialEquations.jl` (Keyword Arguments)](https://docs.sciml.ai/DiffEqDocs/stable/basics/common_solver_opts/)