from typing import Any


def get_substitute_variable(val: str, var_dict: dict) -> Any:
    """Return substitution for variable reference in str, or None if it is not found."""
    var_marker = 'var:'
    if val.startswith(var_marker):
        var_name = val[len(var_marker):]

        if var_name in var_dict:
            return var_dict[var_name]

    return None