For UDFs that allow NULL as input arguments (where the CREATE FUNCTION or REPLACE FUNCTION statement specifies the CALLED ON NULL INPUT clause), simple mapping to Java primitives is not appropriate because they cannot represent NULLs.
To override the default mapping, the EXTERNAL NAME clause in the CREATE FUNCTION or REPLACE FUNCTION statement must explicitly specify the mapping in the parameter list of the Java method. For an example that shows how to override the default mapping, see Example: Overriding Default Parameter Mapping to Handle NULLs.