Function conversion_prefix 

#[doc(hidden)]
pub fn conversion_prefix(
    param: &str,
    nullable: bool,
    expected: Option<&str>,
) -> String

The message prefix of a conversion failure whose expectation comes from the error at run time (see crate::__mx_conversion_expectation!): '<p>' must be <expected> ('<p>' must be NULL or <expected> for an Option<_> parameter, nullable), else invalid '<p>' argument.