GB of zero ideal is 0

Author: Remi Prebet

src/algorithms/groebner-bases.jl

@@ -152,7 +152,7 @@ function _core_groebner_basis(
     F = I.gens
 
     if iszero(F)
-        I.gb[eliminate] = QQMPolyRingElem[]
+        I.gb[eliminate] = length(F)==0 ? F : F[1:1]
         return I.gb[eliminate]
     end
 
@@ -207,6 +207,11 @@ function _core_groebner_basis(
             nr_thrds, max_nr_pairs, 0, la_option, reduce_gb, 0, info_level)
     end
 
+    if nr_terms == 0
+        I.gb[eliminate] = [R(0)]
+        return I.gb[eliminate]
+    end
+
     # convert to julia array, also give memory management to julia
     jl_ld   = gb_ld[]
     jl_len  = Base.unsafe_wrap(Array, gb_len[], jl_ld)