Nodejs AssertionError [ERR_ASSERTION]: You must specify the endpoint url when invoking this module

## Expected Behavior
AssertionError [ERR_ASSERTION]: You must specify the endpoint url when invoking this module
I am suggesting event emitter maybe. I need away for converting dburl() to dburl object

## Current Behavior
I used couchdb and I was wondering If you could help me about differential between

> require("nano")(require("../startup/environment").dburl) <=with=>
> require("nano")(require("../startup/environment").dburl())

It is ok when I set process.env.DB_ADDRESS on line of this code(Bookmark:**********\/**********)

```
const winston = require("winston");
const fs = require("fs");
const result = require("dotenv").config();

if (result.error) {
throw result.error;
}
winston.info(result.parsed);

const doSelectEnv = () => {
switch (process.env.NODE_ENV) {
case "development":
const envConfigDev = require("dotenv").parse(
fs.readFileSync(".env.override.development")
);
for (const k in envConfigDev) {
process.env[k] = envConfigDev[k];
winston.info(process.env[k]);
}
break;
case "production":
const envConfigPro = require("dotenv").parse(
fs.readFileSync(".env.override.production")
);
for (const k in envConfigPro) {
//Bookmark **********\/********** if("DB_ADDRESS" == k) {
// console.log(url);
// }
process.env[k] = envConfigPro[k];
winston.info(process.env[k]);
}
break;
case "stage":
const envConfigStage = require("dotenv").parse(
fs.readFileSync(".env.override.stage")
);
for (const k in envConfigStage) {
process.env[k] = envConfigStage[k];
winston.info(process.env[k]);
}
break;
}
};
exports.doSelectEnv = doSelectEnv;
exports.dburl = "http://dbadmin:server@192.168.1.11:5984"; // process.env.DB_ADDRESS
```

> If I use dburl object it will execute (user.js consume dburl)

```
const db = require("nano")(require("../startup/environment").dburl).use(
"dbvidly"
);
```
## Steps to Reproduce (for bugs)

> But I need this code because of DB_ADDRESS

` exports.dburl = ()=> {return process.env.DB_ADDRESS);`

when I used this code then rising ERR_ASSERTION

```
const db = require("nano")(require("../startup/environment").dburl()).use(
"dbvidly"
);
```

> AssertionError [ERR_ASSERTION]: You must specify the endpoint url when invoking this module

## Your Environment
* Version nodejs: 8.11.1 on container
* executed by nodemon

Start with startup/environment, especially the dburl export, and inspect how user.js invokes nano with dburl versus dburl(). Reproduce the two forms using the reported Node.js 8.11.1 environment and the DB_ADDRESS setup. Done means clearly identifying the invocation difference and documenting or confirming the expected endpoint behavior.

Written by the indexing model from the issue text.