How to not implement a deprecated interface method, which has no default implementation?

In the comment for ExternalDocumentProvider.hasDocumentationFor() it says if not implemented. How is that possible when there is no default implementation?

package com.intellij.lang.documentation;

import com.intellij.openapi.project.Project;
import com.intellij.psi.PsiElement;
import org.jetbrains.annotations.Nls;
import org.jetbrains.annotations.Nullable;

import java.util.List;

public interface ExternalDocumentationProvider {
  /**
   * @deprecated Use/override {@link #fetchExternalDocumentation(Project, PsiElement, List, boolean)} instead.
   */
  @SuppressWarnings("DeprecatedIsStillUsed")
  @Deprecated
  default @Nls @Nullable String fetchExternalDocumentation(final Project project, PsiElement element, List<String> docUrls) {
    return null;
  }

  default @Nls @Nullable String fetchExternalDocumentation(final Project project, PsiElement element, List<String> docUrls, boolean onHover) {
    return fetchExternalDocumentation(project, element, docUrls);
  }

    /**
     * Quick check for existence of external documentation for specified element. Called from action update, so must be fast.
     * If not implemented, update check is performed by calling {@link DocumentationProvider#getUrlFor(PsiElement, PsiElement)}.
     *
     * @deprecated existing implementations fall back to checking for existing url
     * @param element the element to check for existence of documentation
     * @param originalElement the element at caret (on which the action was invoked)
     * @return true if the external documentation action should be enabled, false otherwise.
     */
  @Deprecated
  boolean hasDocumentationFor(PsiElement element, PsiElement originalElement);

  /**
   * Checks if the provider is capable of asking the user to configure external documentation for an element.
   *
   * @param element the element for which no documentation was found
   * @return true if the element is applicable to this provider and the provider has a UI to configure the documentation location, false otherwise
   */
  boolean canPromptToConfigureDocumentation(PsiElement element);

  /**
   * Prompts the user to configure the external documentation for an element if none was found.
   *
   * @param element the element for which no documentation was found
   */
  void promptToConfigureDocumentation(PsiElement element);
}