gh-36634: permutation_normal_form : case of empty matrices
    
fixes #36629

### 📝 Checklist

- [x] The title is concise, informative, and self-explanatory.
- [x] I have linked a relevant issue or discussion.
- [x] I have created tests covering the changes.
    
URL: #36634
Reported by: Frédéric Chapoton
Reviewer(s): Matthias Köppe

Author: Release Manager

src/sage/matrix/matrix2.pyx

@@ -8575,15 +8575,27 @@ cdef class Matrix(Matrix1):
 
         TESTS::
 
+            sage: # needs sage.graphs
             sage: M = matrix(ZZ, [[3, 4, 5], [3, 4, 5], [3, 5, 4], [2, 0,1]])
-            sage: M.permutation_normal_form()                                           # needs sage.graphs
+            sage: M.permutation_normal_form()
             [5 4 3]
             [5 4 3]
             [4 5 3]
             [1 0 2]
+            sage: M = matrix(ZZ, 0, 0, [])
+            sage: M.permutation_normal_form()
+            []
+            sage: M.permutation_normal_form(check=True)
+            ([], ((), ()))
         """
         nrows = self.nrows()
         ncols = self.ncols()
+        if not nrows or not ncols:
+            if not check:
+                return self
+            from sage.groups.perm_gps.permgroup_named import SymmetricGroup
+            return (self, (SymmetricGroup(nrows).one(),
+                           SymmetricGroup(ncols).one()))
 
         # A helper
         def new_sorted_matrix(m):