diff --git a/euphonic/cli/utils.py b/euphonic/cli/utils.py
index 0d96555d..13cb492d 100644
--- a/euphonic/cli/utils.py
+++ b/euphonic/cli/utils.py
@@ -671,7 +671,7 @@ def __call__(self, parser, args, values, option_string=None):
         section.add_argument(
             '-s', '--save-to', dest='save_to', default=None,
             help='Save resulting plot to a file with this name')
-        section.add_argument('--title', type=str, default='',
+        section.add_argument('--title', type=str, default=None,
                              help='Plot title')
         section.add_argument('--x-label', '--xlabel', type=str, default=None,
                              dest='xlabel', help='Plot x-axis label')
@@ -935,8 +935,6 @@ def _compose_style(
     style.append(explicit_args)
     return style
 
-def _get_title(filename: str, title: str = '') -> str:
+def _get_title(filename: str, title: str | None = None) -> str:
     """Get a plot title: either user-provided string, or from filename"""
-    if title:
-        return title
-    return pathlib.Path(filename).stem
+    return pathlib.Path(filename).stem if title is None else title
diff --git a/euphonic/plot.py b/euphonic/plot.py
index 7b427242..6ceb2daa 100644
--- a/euphonic/plot.py
+++ b/euphonic/plot.py
@@ -99,7 +99,7 @@ def plot_1d(spectra: Union[Spectrum1D,
                            Spectrum1DCollection,
                            Sequence[Spectrum1D],
                            Sequence[Spectrum1DCollection]],
-            title: str = '',
+            title: str | None = None,
             xlabel: str = '',
             ylabel: str = '',
             ymin: Optional[float] = None,
@@ -191,7 +191,7 @@ def plot_1d(spectra: Union[Spectrum1D,
     ax.set_xlabel(xlabel)
     ax.set_ylabel(ylabel)
 
-    fig.suptitle(title)
+    fig.suptitle('' if title is None else title)
     return fig
 
 
@@ -249,7 +249,7 @@ def plot_2d(spectra: Union[Spectrum2D, Sequence[Spectrum2D]],
             vmin: Optional[float] = None,
             vmax: Optional[float] = None,
             cmap: Optional[Union[str, Colormap]] = None,
-            title: str = '',
+            title: str | None = None,
             xlabel: str = '',
             ylabel: str = '') -> Figure:
     """
@@ -319,7 +319,7 @@ def _get_minmax_intensity(spectrum: Spectrum2D) -> Tuple[float, float]:
     ax.set_xlabel(xlabel)
     ax.set_ylabel(ylabel)
 
-    fig.suptitle(title)
+    fig.suptitle('' if title is None else title)
 
     return fig
 
diff --git a/euphonic/writers/phonon_website.py b/euphonic/writers/phonon_website.py
index ce5664f3..b4c13154 100644
--- a/euphonic/writers/phonon_website.py
+++ b/euphonic/writers/phonon_website.py
@@ -166,13 +166,15 @@ def _combine_neighbouring_labels(x_tick_labels: XTickLabels) -> XTickLabels:
     for index in sorted(labels):
         if index - 1 in labels:
             if labels.get(index - 1) != labels.get(index):
+                # Neighbouring labels are different: merge second into first
                 labels[index - 1] = f"{labels[index - 1]}|{labels[index]}"
+            # Remove second label of pair
             del labels[index]
     return sorted(labels.items())
 
 
 def _modes_to_phonon_website_dict(modes: QpointPhononModes,
-                                  name: str = 'Euphonic export',
+                                  name: str | None = None,
                                   repetitions: tuple[int, int, int] = (2, 2, 2),
                                   x_tick_labels: XTickLabels | None = None,
                                   ) -> PhononWebsiteData: