This is the full strack trace:
g: Non [a-z0-9/._-] character in path of location: minecraft:CaveSpider
at ns.<init>(SourceFile:36) ~inecraft_server.17w50a.jar:?]
at ns.<init>(SourceFile:41) ~inecraft_server.17w50a.jar:?]
at aru.g(SourceFile:42) ~inecraft_server.17w50a.jar:?]
at aru.b(SourceFile:185) ~inecraft_server.17w50a.jar:?]
at bbf.a(SourceFile:86) ~inecraft_server.17w50a.jar:?]
at bds.a(SourceFile:287) ~inecraft_server.17w50a.jar:?]
at bds.a(SourceFile:124) inecraft_server.17w50a.jar:?]
at rn.c(SourceFile:141) inecraft_server.17w50a.jar:?]
at rn.a(SourceFile:160) inecraft_server.17w50a.jar:?]
at ro.a(SourceFile:871) inecraft_server.17w50a.jar:?]
at net.minecraft.server.MinecraftServer.a(SourceFile:425) inecraft_server.17w50a.jar:?]
at net.minecraft.server.MinecraftServer.j_(SourceFile:450) inecraft_server.17w50a.jar:?]
at net.minecraft.server.MinecraftServer.run(SourceFile:544) inecraft_server.17w50a.jar:?]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_111]