Allow trailing commas, or find distinction between blocks and dicts with one element.

[OAGr]

Description of suggestion or shortcoming:

From: https://squigglehub.org/models/mlao-pdx/trailing-comma

The issue shows up in the last two assignments of this script (mlao-pdx/trailing-comma):

    Run as-is, and all is good
    Format the code, and it removes the unnecessary block from line 32, and removes the trailing commas from lines 29 and 35, but leaves the block.
    Runtime error occurs on line 35 as a block is not a dictionary and cannot be merged
    Format again, and the block disappears as it did for db.
    Runtime error occurs on line 35 as an expression is not a dictionary and cannot be merged
    By now it is difficult to detect what actually happened...
    Request/suggestion:
        Allow trailing commas, because:
        Easy single attribute dictionaries
        Multi-entry dictionaries and lists re-ordering without juggling trailing commas