[Solved] A value of type ‘Null’ can’t be assigned to a parameter of type ‘Key’ in a const constructor. Try using a subtype, or removing the keyword ‘const’

A value of type ‘Null’ can’t be assigned to a parameter of type ‘Key’ in a const constructor. Try using a subtype, or removing the keyword ‘const’

solved A value of type ‘Null’ can’t be assigned to a parameter of type ‘Key’ in a const constructor. Try using a subtype, or removing the keyword ‘const’