Fixing bug with quotients by trivial ideals.

src/sage/algebras/lie_algebras/quotient.py

@@ -274,6 +274,7 @@ def __init__(self, I, L, names, index_set, category=None):
         self._ambient = L
         self._I = I
         self._sm = sm
+        self._triv_ideal = bool(I.dimension() == 0)
 
         LieAlgebraWithStructureCoefficients.__init__(
             self, L.base_ring(), s_coeff, names, index_set, category=category)
@@ -426,14 +427,23 @@ def from_vector(self, v, order=None, coerce=False):
             sage: el.parent() == Q
             True
 
-        An element from a vector of the ambient module
+        An element from a vector of the ambient module::
 
             sage: el = Q.from_vector([1, 2, 3]); el
             -2*X - Y
             sage: el.parent() == Q
             True
+
+        Check for the trivial ideal::
+
+            sage: L.<x,y,z> = LieAlgebra(GF(3), {('x','z'): {'x':1, 'y':1}, ('y','z'): {'y':1}})
+            sage: I = L.ideal([])
+            sage: Q = L.quotient(I)
+            sage: v = Q.an_element().to_vector()
+            sage: Q.from_vector(v)
+            x + y + z
         """
-        if len(v) == self.ambient().dimension():
+        if not self._triv_ideal and len(v) == self.ambient().dimension():
             return self.retract(self.ambient().from_vector(v))
 
         return super().from_vector(v)