add conversion for pandas NA to missing

Author: Christopher Doris

src/PythonCall.jl

@@ -42,6 +42,7 @@ include("concrete/datetime.jl")
 include("concrete/code.jl")
 include("concrete/ctypes.jl")
 include("concrete/numpy.jl")
+include("concrete/pandas.jl")
 # @py
 # anything below can depend on @py, anything above cannot
 include("py_macro.jl")
@@ -107,8 +108,9 @@ function __init__()
         init_gui()
         init_ipython()
         init_tables()
-        init_numpy()
         init_ctypes()
+        init_numpy()
+        init_pandas()
     end
     @require PyCall="438e738f-606a-5dbb-bf0a-cddfbfd45ab0" init_pycall(PyCall)
 end

src/concrete/pandas.jl

@@ -0,0 +1,7 @@
+pyconvert_rule_pandas_na(::Type{Nothing}, x::Py) = pyconvert_return(nothing)
+pyconvert_rule_pandas_na(::Type{Missing}, x::Py) = pyconvert_return(missing)
+
+function init_pandas()
+    pyconvert_add_rule("pandas._libs.missing:NAType", Missing, pyconvert_rule_pandas_na, PYCONVERT_PRIORITY_CANONICAL)
+    pyconvert_add_rule("pandas._libs.missing:NAType", Nothing, pyconvert_rule_pandas_na)
+end