A Corgi is a short-legged dog represented by a dataclass with the fields:

• name (a string)
• height (an integer)
• coat_color (a string, either 'yellow' or 'mixed')

A Tree is an empty dataclass, and the instance EMPTY represents an empty tree.

A FamilyTree is a dataclass inheriting from Tree that represents the known lineage of a Corgi, with the fields:

• corgi (a Corgi)
• mother (a Tree)
• father (a Tree)

The function stack_yellow_corgis below is meant to calculate the total height of the yellow Corgis in a lineage. Fill in the blanks inside the function definition to complete the code.