added nonnull assertions

src/main/java/carpet/script/exception/package-info.java

@@ -0,0 +1,8 @@
+@ParametersAreNonnullByDefault
+@FieldsAreNonnullByDefault
+@MethodsReturnNonnullByDefault
+package carpet.script.exception;
+
+import net.minecraft.FieldsAreNonnullByDefault;
+import net.minecraft.MethodsReturnNonnullByDefault;
+import javax.annotation.ParametersAreNonnullByDefault;