getdoc returns nothing when given null

Author: Christopher Doris

src/Py.jl

@@ -451,7 +451,8 @@ Base.powermod(x::Number, y::Py, z::Number) = pypow(x, y, z)
 Base.powermod(x::Py, y::Number, z::Number) = pypow(x, y, z)
 
 # documentation
-function Base.Docs.getdoc(x::Py, @nospecialize(sig))
+function Base.Docs.getdoc(x::Py, @nospecialize(sig)=Union{})
+    pyisnull(x) && return nothing
     parts = []
     inspect = pyimport("inspect")
     # head line

test/abstract.jl

@@ -207,6 +207,12 @@
         @test !pyin(-1, x)
         @test !pyin(pybuiltins.None, x)
     end
+    @testset "getdoc" begin
+        @test Base.Docs.getdoc(Py(nothing)) isa Markdown.MD
+        @test Base.Docs.getdoc(Py(12)) isa Markdown.MD
+        @test Base.Docs.getdoc(pybuiltins.int) isa Markdown.MD
+        @test Base.Docs.getdoc(PythonCall.PyNULL) === nothing
+    end
 end
 
 @testset "iter" begin

test/runtests.jl

@@ -1,4 +1,4 @@
-using PythonCall, Test, Dates, Aqua
+using PythonCall, Test, Dates, Aqua, Markdown
 
 # The unbound_args test fails on methods with signature like foo(::Type{Tuple{Vararg{V}}}) where V
 # Seems like a bug.