show_doc does not display return value docment for function/method with no arguments

Example from the documentation:
``` python
class Adder:
"An addition calculator"
def __init__(self,
a:int, # First operand
b:int, # 2nd operand
): self.a,self.b = a,b

def calculate(self
)->int: # Integral result of addition operator
"Add `a` to `b`"
return a+b

show_doc(Adder.calculate)
```

I would expect there to be a table entry with "Integral result of addition operator".

Reproduce the documented Adder example and call show_doc(Adder.calculate) to confirm that the return annotation is missing. Start by tracing the show_doc entry point and its handling of methods with no arguments; done means the output includes "Integral result of addition operator" in the return-value table.

Written by the indexing model from the issue text.