Fix string methods to handle empty values (#4442)

* Enable strings category methods tests

* Ensure escape, pad, padEnd, padStart, trim, trimEnd, trimStart, unescape return an empty string for falsey values

* Coerce value to string using toString in truncate, capitalize and case methods

* Ensure createCaseFirst returns an empty string for falsey values

camelCase.js

@@ -1,5 +1,6 @@
 import upperFirst from './upperFirst.js'
 import words from './words.js'
+import toString from './toString.js'
 
 /**
  * Converts `string` to [camel case](https://en.wikipedia.org/wiki/CamelCase).
@@ -21,7 +22,7 @@ import words from './words.js'
  * // => 'fooBar'
  */
 const camelCase = (string) => (
-  words(`${string}`.replace(/['\u2019]/g, '')).reduce((result, word, index) => {
+  words(toString(string).replace(/['\u2019]/g, '')).reduce((result, word, index) => {
     word = word.toLowerCase()
     return result + (index ? upperFirst(word) : word)
   }, '')