port 2.5.4: Error: Unable to open port: invalid command name "compiler.cxx_standard"

[nikgervae]

I am on MacOS High Sierra 10.13.6, trying to update my ports. I ran "sudo port selfupdate" and then, I ran "sudo port upgrade outdated" and got this output:
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Error: Unable to open port: invalid command name "compiler.cxx_standard"
Error: Follow ​https://guide.macports.org/#project.tickets to report a bug.
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If I try "sudo port upgrade installed", I instead get this error:
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Error: Unable to open port: can't set "compiler.blacklist": invalid command name "compiler.command_line_tools_version"
Error: Follow ​https://guide.macports.org/#project.tickets to report a bug.
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