Due to the way Fluid Registration works and the vagaries of mod load order, having two mods defining the same Fluid can result in save breaking issues. For that reason is recommended that mods provide a config to disable Fluid registration so that the user can reduce to the number of mods defining a Fluid to one.
It's ok to throw an error if no mod eventually defines the Fluid, but the option must be available or you can result in broken worlds (missing blocks/other issues).
Additionally, you should always request Fluid objects directly from the Fluid Registry. Don't store them in static variables. You can never be sure that you have the final version if you don't do this.
Due to the way Fluid Registration works and the vagaries of mod load order, having two mods defining the same Fluid can result in save breaking issues. For that reason is recommended that mods provide a config to disable Fluid registration so that the user can reduce to the number of mods defining a Fluid to one.
It's ok to throw an error if no mod eventually defines the Fluid, but the option must be available or you can result in broken worlds (missing blocks/other issues).
Additionally, you should always request Fluid objects directly from the Fluid Registry. Don't store them in static variables. You can never be sure that you have the final version if you don't do this.
Example of kinds of issues that can occur: http://imgur.com/lyvkxbm