You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: validation_deps.rs
    path of file: ./repos/holochain/crates/holochain/src/core/workflow/sys_validation_workflow
    
    the code of the file until where you have to start completion: use holo_hash::ActionHash;
use holochain_cascade::CascadeSource;
use holochain_zome_types::{
    record::{Record, SignedActionHashed},
    Action,
};
use std::collections::{HashMap, HashSet};

/// A collection of validation dependencies for the current set of DHT ops requiring va
    
    pub fn set_action(&mut self, action: SignedActionHashed) {
        match self.dependency {
            None => {
                self.dependency = Some(ValidationDependency {
                    signed_action: action,
                    fetched_from: CascadeSource::Network,
                });
            }
            _ => {
                tracing::warn!("Attempted to set a record on a dependency that already has a value, this is a bug")
            }
        }
    }