code: Description createErrorDescriptionForNullAssignment(
        ErrorMessage errorMessage,
        @Nullable Tree suggestTreeIfCastToNonNull,
        @Nullable TreePath suggestTreePathIfSuppression,
        Description.Builder descriptionBuilder) {
      final Tree enclosingSuppressTree = suppressibleNode(suggestTreePathIfSuppression);
      if (config.getCastToNonNullMethod() != null) {
        return createErrorDescription(errorMessage, suggestTreeIfCastToNonNull, descriptionBuilder);
      } else {
        return createErrorDescription(errorMessage, enclosingSuppressTree, descriptionBuilder);
      }
    }
docs: create an error description for a generalized @Nullable value to @NonNull location assignment.
  
  <p>This includes: field assignments, method arguments and method returns
  
  @param errorMessage the error message object.
  @param suggestTreeIfCastToNonNull the location at which a fix suggestion should be made if a
  castToNonNull method is available (usually the expression to cast)
  @param suggestTreePathIfSuppression the location at which a fix suggestion should be made if a
  castToNonNull method is not available (usually the enclosing method, or any place
  where @SuppressWarnings can be added).
  @param descriptionBuilder the description builder for the error.
  @return the error description.