Crash in webrev command

$ git skara webrev HEAD~1..HEAD
Exception in thread "main" java.nio.file.NoSuchFileException: HEAD~1..HEAD
at java.base/sun.nio.fs.UnixException.translateToIOException(UnixException.java:92)
at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:106)
at java.base/sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:111)
at java.base/sun.nio.fs.UnixFileSystemProvider.newByteChannel(UnixFileSystemProvider.java:219)
at java.base/java.nio.file.Files.newByteChannel(Files.java:375)
at java.base/java.nio.file.Files.newByteChannel(Files.java:426)
at java.base/java.nio.file.spi.FileSystemProvider.newInputStream(FileSystemProvider.java:420)
at java.base/java.nio.file.Files.newInputStream(Files.java:160)
at java.base/java.nio.file.Files.newBufferedReader(Files.java:2916)
at java.base/java.nio.file.Files.readAllLines(Files.java:3396)
at java.base/java.nio.file.Files.readAllLines(Files.java:3436)
at org.openjdk.skara.cli/org.openjdk.skara.cli.GitWebrev.generate(GitWebrev.java:401)
at org.openjdk.skara.args/org.openjdk.skara.args.Command.main(Command.java:54)
at org.openjdk.skara.args/org.openjdk.skara.args.MultiCommandParser.lambda$parse$3(MultiCommandParser.java:66)
at org.openjdk.skara.cli/org.openjdk.skara.cli.GitWebrev.main(GitWebrev.java:502)
at org.openjdk.skara.cli/org.openjdk.skara.cli.GitSkara.main(GitSkara.java:231)