[1.8.8] Error occurred while enabling Sentinel

[HowardZHY]

The output of command /version on my server is: (PaperSpigot 1.8.8)
The output of command /version citizens on my server is: (Citizens v2.0.35-SNAPSHOT (build 3478))
The output of command /version sentinel on my server is: (v2.9.1-SNAPSHOT (build 525))
A pastebin.com link to my (full!) Sentinel/config.yml file is: (UNRELATED)

java.lang.NoClassDefFoundError: org/bukkit/Particle at org.mcmonkey.sentinel.utilities.SentinelAPIBreakageFix.<clinit>(SentinelAPIBreakageFix.java:31) ~[?:?] at org.mcmonkey.sentinel.targeting.SentinelTarget.<clinit>(SentinelTarget.java:49) ~[?:?] at org.mcmonkey.sentinel.utilities.SentinelVersionCompat.<clinit>(SentinelVersionCompat.java:72) ~[?:?] at org.mcmonkey.sentinel.SentinelPlugin.onEnable(SentinelPlugin.java:317) ~[?:?] at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:321)

org/bukkit/Particle was added in 1.9, it doesn't exist in 1.8.8, please move the Particle type field to another class that won't be loaded