Add guards on null active eigenvalues (#1102)

There were no guards on the active eigenvalues. So if someone selected to define eigenvalues, but didn't (leaving all as -1), it raised errors regarding reshaping a null-size array.

src/aiidalab_qe/app/configuration/advanced/hubbard/hubbard.py

@@ -39,10 +39,12 @@ def render(self):
         )
 
         self.eigenvalues_help = ipw.HTML("""
-            <div style="line-height: 1.4; margin-bottom: 5px;">
+            <div style="line-height: 1.4; margin: 10px 0 5px;">
                 For transition metals and lanthanoids, the starting eigenvalues can be defined (magnetic calculation).
                 <br>
-                It is useful to suggest the desired orbital occupations when the default choice takes another path.
+                It is useful to suggest the desired orbital occupations  when the default choice takes another path.
+                <br>
+                To do so, tick the checkbox below and set the desired eigenvalues to a value other than -1 (unset).
             </div>
         """)
         self.define_eigenvalues_checkbox = ipw.Checkbox(

src/aiidalab_qe/app/configuration/advanced/hubbard/model.py

@@ -66,16 +66,22 @@ def update(self, specific=""):  # noqa: ARG002
             self.needs_eigenvalues_widget = len(self.applicable_kind_names) > 0
 
     def get_active_eigenvalues(self):
-        active_eigenvalues = [
-            orbital_eigenvalue
-            for element_eigenvalues in self.eigenvalues
-            for spin_row in element_eigenvalues
-            for orbital_eigenvalue in spin_row
-            if orbital_eigenvalue[-1] != -1
-        ]
+        if not (
+            active_eigenvalues := [
+                orbital_eigenvalue
+                for element_eigenvalues in self.eigenvalues
+                for spin_row in element_eigenvalues
+                for orbital_eigenvalue in spin_row
+                if orbital_eigenvalue[-1] != -1
+            ]
+        ):
+            return []
         eigenvalues_array = np.array(active_eigenvalues, dtype=object)
-        new_shape = (np.prod(eigenvalues_array.shape[:-1]), 4)
-        return eigenvalues_array.reshape(new_shape).tolist()
+        new_shape = (int(np.prod(eigenvalues_array.shape[:-1])), 4)
+        return [
+            tuple(eigenvalue)
+            for eigenvalue in eigenvalues_array.reshape(new_shape).tolist()
+        ]
 
     def set_active_eigenvalues(self, eigenvalues: list):
         eigenvalues_array = np.array(eigenvalues, dtype=object)

tests/configuration/test_advanced.py

@@ -172,7 +172,7 @@ def test_advanced_hubbard_settings(generate_structure_data):
     Co_spin_down_row.children[5].value = "1"
 
     assert model.get_active_eigenvalues() == [
-        [1, 1, "Co", 1],
-        [3, 1, "Co", 1],
-        [5, 1, "Co", 1],
+        (1, 1, "Co", 1),
+        (3, 1, "Co", 1),
+        (5, 1, "Co", 1),
     ]