fix PyNULL typo (#544)

* fix PyNULL typo

* simplify PyObjectArray finalizer gc test

---------

Co-authored-by: Christopher Doris <github.com/cjdoris>

Author: ericphanson

Diff for: src/GC/GC.jl

@@ -103,7 +103,7 @@ function enqueue(ptr::C.PyPtr)
 end
 
 function enqueue_all(ptrs)
-    if any(!=(C.PYNULL), ptrs) && C.CTX.is_initialized
+    if any(!=(C.PyNULL), ptrs) && C.CTX.is_initialized
         if C.PyGILState_Check() == 1
             for ptr in ptrs
                 if ptr != C.PyNULL

Diff for: test/JlWrap.jl

@@ -577,4 +577,13 @@ end
         @test pyeq(Bool, x.count(nothing), 0)
         @test pyeq(Bool, x.count("2"), 0)
     end
+
+    @testset "PyObjectArray" begin
+        # https://github.com/JuliaPy/PythonCall.jl/issues/543
+        # Here we check the finalizer does not error
+        # We must not reuse `arr` in this code once we finalize it!
+        let arr = PyObjectArray([1, 2, 3])
+            finalize(arr)
+        end
+    end
 end