Straight Blade Katana

Hello,
A straight bladed mumei katana is coming up for auction soon in my state. Is it highly unusual to come across a straight bladed Katana? I saw a T.V. show recently where I belive one of Japan's national treasure swordsmiths was forgeing a straight blade for the Emperor.
Any comments are welcome, I am wondering if it is worth the drive.

Bob

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condition

From what I can see in the pictures, the condition is "rough". Also, it appears that it may have a bit of a curve?
A straight-blade katana/tachi is unusual, but not necessarily valuable.
I would not pay a high price for it.

Pete