nullable_type_in_extends_clause
A class can't extend a nullable type.
Description
#The analyzer produces this diagnostic when a class declaration uses an extends
clause to specify a superclass, and the superclass is followed by a ?
.
It isn't valid to specify a nullable superclass because doing so would have no meaning; it wouldn't change either the interface or implementation being inherited by the class containing the extends
clause.
Note, however, that it is valid to use a nullable type as a type argument to the superclass, such as class A extends B<C?> {}
.
Example
#The following code produces this diagnostic because A?
is a nullable type, and nullable types can't be used in an extends
clause:
class A {}
class B extends A? {}
Common fixes
#Remove the question mark from the type:
class A {}
class B extends A {}
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