How do I convert a non-closed line (think of it as a C) to a polygon filling the area in ArcMap?

I think I can convert a ring to a polygon with the Construct Polygon function on the Advanced Editing Toolbar. However I get the following error: "No polygons were created. Ensure the selected features form continuous rings and overlap the polygons."

Obviously, I need to make my C into an O. It's just a matter of adding a line segment between the two endpoints. How do I add that segment and make the line into a ring?

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    How good are you at python, VB.net or C#? You could fumble through it by feature vertices to points (both ends), add XY coordinates, export to a table then points to lines to close the gaps by going directly from start-end (or end-start) but this would be a lot better with code.. if you have some please post it. – Michael Stimson May 30 '18 at 1:19
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    Make it an answer perhaps? – Joooeey May 30 '18 at 1:27
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    If my comment has helped you come to an answer feel free to expand with your methods, pictures and links to answer your own question and I'll upvote it. – Michael Stimson May 30 '18 at 1:46
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    Convert line to vertices, points to line (close), result to polygon. Script is a last resort. – FelixIP May 30 '18 at 3:54

A manual solution was suggested by Michael Stimson in a comment to the Q:

  • Use Feature Vertices to Points (Data Management) to convert the line into a list of points
  • Use Points to Line (Data Management) and tick Close Line to get a ring.
  • Activate edit mode by clicking Editor > Start editing on the Editor toolbar. Select a target layer that supports polygons. This does not have to be the source layer with your ring (line).
  • Select the ring and convert it to a polygon with the Construct Polygon function on the Advanced Editing toolbar.

I accessed the first two functions from the search button which is usually on the right of the screen.

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