fixing different configuration option for navigation

vizro-core/src/vizro/models/_navigation/_navigation_utils.py

@@ -8,14 +8,17 @@ def _validate_pages(pages):
     from vizro.models import Page
 
     pages_as_list = list(itertools.chain(*pages.values())) if isinstance(pages, dict) else pages
-
-    if not pages_as_list:
-        raise ValueError("Ensure this value has at least 1 item.")
-
     # Ideally we would use dash.page_registry or maybe dashboard.pages here, but we only register pages in
     # dashboard.pre_build and model manager cannot find a Dashboard at validation time.
     # page[0] gives the page model ID.
     registered_pages = [page[0] for page in model_manager._items_with_type(Page)]
+
+    if pages is None:
+        return registered_pages
+
+    if not pages_as_list:
+        raise ValueError("Ensure this value has at least 1 item.")
+
     if unknown_pages := [page for page in pages_as_list if page not in registered_pages]:
         raise ValueError(f"Unknown page ID {unknown_pages} provided to argument 'pages'.")
     return pages

vizro-core/src/vizro/models/_navigation/nav_bar.py

@@ -8,6 +8,7 @@
 
 from vizro.models import VizroBaseModel
 from vizro.models._models_utils import _log_call
+from vizro.models._navigation._navigation_utils import _validate_pages
 from vizro.models._navigation.nav_item import NavItem
 from vizro.models.types import NavPagesType
 
@@ -24,6 +25,9 @@ class NavBar(VizroBaseModel):
     pages: Optional[NavPagesType] = None
     items: List[NavItem] = []
 
+    # validators
+    _validate_pages = validator("pages", allow_reuse=True, pre=True, always=True)(_validate_pages)
+
     @validator("items", always=True)
     def validate_items(cls, items, values):
         if not items:

vizro-core/src/vizro/models/_navigation/nav_item.py

@@ -48,7 +48,7 @@ def pre_build(self):
         if self.tooltip is None:
             if self.text and len(self.text) > self.max_text_length:
                 self.tooltip = self.text
-                self.text = self.text[:self.max_text_length]
+                self.text = self.text[: self.max_text_length]
 
     @validator("text", always=True)
     def set_text(cls, text, values):
@@ -69,9 +69,7 @@ def build(self, active_page_id):
             list(itertools.chain(*self.pages.values()))[0] if isinstance(self.pages, dict) else self.pages[0]
         )
         icon_div = (
-            html.Span(self.icon, className="material-symbols-outlined")
-            if self.icon
-            else html.Div(className="hidden")
+            html.Span(self.icon, className="material-symbols-outlined") if self.icon else html.Div(className="hidden")
         )
         text_div = html.Div(children=[self.text], className="icon-text") if self.text else html.Div(className="hidden")
 

vizro-core/src/vizro/models/_navigation/navigation.py

@@ -27,9 +27,9 @@ class Navigation(VizroBaseModel):
     selector: Optional[NavSelectorType] = None
 
     # validators
-    _validate_pages = validator("pages", allow_reuse=True)(_validate_pages)
+    _validate_pages = validator("pages", allow_reuse=True, pre=True, always=True)(_validate_pages)
 
-    @validator("selector", pre=True, always=True)
+    @validator("selector", always=True)
     def set_selector(cls, selector, values):
         if selector is None:
             return Accordion(pages=values.get("pages"))