Returns the metadata for the currently validated value.
With the core implementation, this method returns a {@link Mapping\ClassMetadata} instance if the current value is an object, a {@link Mapping\PropertyMetadata} instance if the current value is the value of a property and a {@link Mapping\GetterMetadata} instance if the validated value is the result of a getter method.
If the validated value is neither of these, for example if the validator has been called with a plain value and constraint, this method returns null.
MetadataInterface|null The metadata of the currently validated value.
public function getMetadata();