private boolean isVoid(Type returnType) {
		boolean result = false;
		if (Void.TYPE.equals(returnType) || Void.class.equals(returnType))
			result = true;
		else if (returnType instanceof ParameterizedType parameterizedType) {
			Type[] types = parameterizedType.getActualTypeArguments();
			if (types != null && isResponseTypeWrapper(ResolvableType.forType(returnType).getRawClass()))
				result = isVoid(types[0]);
		}
		return result;
	}
Is void boolean.

@param returnType the return type
@return the boolean
springdoc-openapi-starter-common/src/main/java/org/springdoc/core/service/GenericResponseService.java