Add explicit check for empty ekos

src/pineko/theory.py

@@ -20,6 +20,10 @@
 logger = logging.getLogger(__name__)
 
 
+class EmptyEkoError(Exception):
+    """Raised if the loaded eko is empty."""
+
+
 def check_scvar_evolve(grid, max_as, max_al, kind: check.Scale):
     """Check scale variations and central orders consistency."""
     available, max_as_effective = check.contains_sv(grid, max_as, max_al, kind)
@@ -404,6 +408,9 @@ def fk(self, name, grid_path, tcard, pdf):
                 check_scvar_evolve(grid, max_as, max_al, check.Scale.FACT)
         # loading ekos to produce a tmp copy
         with eko.EKO.read(eko_filename) as operators:
+            # Skip the computation of the fktable if the eko is empty
+            if len(operators.mu2grid) == 0:
+                raise EmptyEkoError
             eko_tmp_path = operators.paths.root.parent / "eko-tmp.tar"
             operators.deepcopy(eko_tmp_path)
         with eko.EKO.edit(eko_tmp_path) as operators: