So I'm getting into this revolve issue and I feel like I'm missing something because the results are inconsistent.  I'm trying to create a semi-circle object below with thin but the thin also creates a centerline on the bottom per shown image.

However, when I tried to create the revolve without the center line like the below image.

I thought I can create a half revolving object without the middle line because it works prior. It came up with pop up that asked the question to close the sketch.  I said no. 

Then error " Sketch is open, self-intersecting, or intersects the centerline".

I can't seem to repeat what I did anymore.  Is there something I miss in the rule of creating revolve?  From the picture above, what did I do wrong or not follow?  I did what others did per some of the instructions on youtube, like this.  Nothing is different on what I did with what he did and yet mine doesn't work.  Please advise?

SolidWorks Tutorial Sheet Metal Cone - YouTube 

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Solidworks 2019 SP4