the error in the log without breaking client
http://hastebin.com/qesisitixi.avrasm

I can't access that paste, can you remake it please?

http://paste.ubuntu.com/13227089/
:)

I expect that this is when hovering over a clipping? could you tell me what plant this clipping is from?

no. This error occurs only when I go to the server. without any action.
sorry I do not know much english.

That is not possible, this line in the log:

at com.InfinityRaider.AgriCraft.handler.ItemToolTipHandler.addSeedStatsTooltip(ItemToolTipHandler.java:28) ~[ItemToolTipHandler.class:?]

is ClientSide only code:
https://github.com/InfinityRaider/AgriCraft/blob/master/src/main/java/com/InfinityRaider/AgriCraft/handler/ItemToolTipHandler.java#L18
https://github.com/InfinityRaider/AgriCraft/blob/master/src/main/java/com/InfinityRaider/AgriCraft/proxy/ClientProxy.java#L98-L99

And it also says client thread:

[Client thread/ERROR]

So when does it happen?

Yes that's right. the error in the log on the client side.

Actually, some mod seems to be searching the ItemRegistry, including tooltips:

at stevesaddons.threading.SearchItems.setItems(SearchItems.java:82) [SearchItems.class:?]
at stevesaddons.network.message.SearchRegistryGenerateMessage.onMessage(SearchRegistryGenerateMessage.java:29) [SearchRegistryGenerateMessage.class:?]

And because a clipping without NBT doesn't make sense this is happening.

I'll add a check to see if there is NBT present or not to prevent this from happening.

When I go to the server.
but it does not break the client and server.
thank. I will wait for the new version and check