The method getDefinitions() does not exist on Digia\GraphQL\Language\AST\Node\NodeInterface. It seems like you code against a sub-type of Digia\GraphQL\Language\AST\Node\NodeInterface such as Digia\GraphQL\Language\AST\Node\DocumentNode.
(
Ignorable by Annotation
)
If this is a false-positive, you can also ignore this issue in your code via the ignore-call annotation