Fix ancient typo in get_order (#246)

Co-authored-by: Orjan Ameye <[email protected]>

Author: david-pl

src/cumulant_expansion.jl

@@ -313,7 +313,7 @@ end
 get_order(::Number) = 0
 get_order(q::QMul) = length(q.args_nc)
 function get_order(q::QAdd)
-    order = Int[get_order(arg) for arg in SymbolicUtils.arguments(t)]
+    order = Int[get_order(arg) for arg in SymbolicUtils.arguments(q)]
     return maximum(order)
 end
 get_order(::QSym) = 1

test/test_average.jl

@@ -64,4 +64,6 @@ using Test
         cumulant_expansion(average(a*b*c*d), 3),
     )
 
+@test get_order(a*b + c) == 2
+
 end # testset