Handle zero ideal cases

Author: Remi Prebet

src/algorithms/groebner-bases.jl

@@ -150,12 +150,13 @@ function _core_groebner_basis(
         )
 
     F = I.gens
-    R = first(F).parent
 
-    if F == repeat([R(0)], length(F))
-        I.gb[eliminate] = F
-        return F
+    if iszero(F)
+        I.gb[eliminate] = QQMPolyRingElem[]
+        return I.gb[eliminate]
     end
+
+    R = first(F).parent
     nr_vars     = nvars(R)
     nr_gens     = length(F)
     field_char  = Int(characteristic(R))
@@ -214,7 +215,7 @@ function _core_groebner_basis(
     #  coefficient handling depending on field characteristic
     if field_char == 0
         ptr     = reinterpret(Ptr{BigInt}, gb_cf[])
-        jl_cf   = [QQFieldElem(unsafe_load(ptr, i)) for i in 1:nr_terms]
+        jl_cf   = QQFieldElem[QQFieldElem(unsafe_load(ptr, i)) for i in 1:nr_terms]
     else
         ptr     = reinterpret(Ptr{Int32}, gb_cf[])
         jl_cf   = Base.unsafe_wrap(Array, ptr, nr_terms)