Revise wording on state visualization filename arg

Author: mtreinish

qiskit/visualization/state_visualization.py

@@ -48,7 +48,7 @@ def plot_state_hinton(state, title="", figsize=None, ax_real=None, ax_imag=None,
         title (str): a string that represents the plot title
         figsize (tuple): Figure size in inches.
         filename (str | None): The optional file path to save image to. If not specified
-            no file is created for the visualization. If this is not ``None`` the return
+            no file is created for the visualization. If this is set the return
             from this function will be ``None``.
         ax_real (matplotlib.axes.Axes): An optional Axes object to be used for
             the visualization output. If none is specified a new matplotlib
@@ -284,7 +284,7 @@ def plot_bloch_multivector(
         title_pad (float): Padding for the title (suptitle ``y`` position is ``0.98``
         and the image height will be extended by ``1 + title_pad/100``).
         filename (str | None): The optional file path to save image to. If not specified
-            no file is created for the visualization. If this is not ``None`` the return
+            no file is created for the visualization. If this is set the return
             from this function will be ``None``.
 
     Returns:
@@ -409,7 +409,7 @@ def plot_state_city(
             Additionally, if specified there will be no returned Figure since
             it is redundant.
         filename (str | None): The optional file path to save image to. If not specified
-            no file is created for the visualization. If this is not ``None`` the return
+            no file is created for the visualization. If this is set the return
             from this function will be ``None``.
 
     Returns:
@@ -651,7 +651,7 @@ def plot_state_paulivec(state, title="", figsize=None, color=None, ax=None, *, f
             Figure will be created and used. Additionally, if specified there
             will be no returned Figure since it is redundant.
         filename (str | None): The optional file path to save image to. If not specified
-            no file is created for the visualization. If this is not ``None`` the return
+            no file is created for the visualization. If this is set the return
             from this function will be ``None``.
 
     Returns:
@@ -838,7 +838,7 @@ def plot_state_qsphere(
         use_degrees (bool): An optional boolean indicating whether to use
             radians or degrees for the phase values in the plot.
         filename (str | None): The optional file path to save image to. If not specified
-            no file is created for the visualization. If this is not ``None`` the return
+            no file is created for the visualization. If this is set the return
             from this function will be ``None``.