<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def merge_section(key, prnt_sec, child_sec):
 """ Synthesize a output numpy docstring section. Parameters key: str The numpy-section being merged. prnt_sec: Optional[str] The docstring section from the parent's attribute. child_sec: Optional[str] The docstring section from the child's attribute. Returns ------- Optional[str] The output docstring section."""

    if prnt_sec is None and child_sec is None:
        return None

    if key == "Short Summary":
        header = ''
    else:
        header = "\n".join((key, "".join("-" for i in range(len(key))), ""))

    if child_sec is None:
        body = prnt_sec
    else:
        body = child_sec

    return header + body