An RNA path is mandatory for RNA_path_from_ID_to_property and for EffectorWeights, this has to provided using RNA_def_struct_path_func (since this struct is shared across ParticleSettings, Modifiers and Rigid Body World). Without this, the animation system cannot work and e.g. keyframes cannot be inserted.

The case for Rigid Body World in rna_EffectorWeight_path was missing, now added.

Rigid Body World Field Weights are capable of being animated, tested with file from T80131 (e.g. gravity, wind).