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Check if there is no nexus running. If not, delete
checkState()is Static convenience methods that help a method or constructor check whether it was invoked correctly (whether its preconditions have been met). This occurs when the precondition does not met.
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java.lang.IllegalStateException: The path to the driver executable must be set by the webdriver.gecko.driver system property; for more information, see https://github.com/mozilla/geckodriver. The latest version can be downloaded from https://github.com/mozilla/geckodriver/releases