Inconsistent errors for functions

When using functions, MappingWeaver throws an error when a function (name) cannot be found, i.e., when it is neither a default function nor a loaded one. On missing parameters, however, to error is raised, which can result in hidden mistakes (triples dropped because a parameter was perceived as NULL).

Start by locating the function resolution and parameter-handling entry points in MappingWeaver. Compare the missing-function and missing-parameter paths, then verify that missing parameters produce an error rather than silently dropping triples; the issue does not name specific files or tests.