fatal: ambiguous argument 'kernel' error

I am attempting to compile an AOSP kernel using a guide from Android's official website/wiki itself. Part of the guide instructs to run the command:

Code:

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git log --max-count=1 kernel

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however I'm getting the following message when I run that:

Code:

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fatal: ambiguous argument 'kernel': unknown revision or path not in the working tree.
Use '--' to separate paths from revisions, like this:
'git <command> [<revision>...] -- [<file>...]'

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I'm building for the Nexus 5 (hammerhead). I have absolutely no prior knowledge for kernel development and I'm wondering what to include to not make the command ambiguous?