/**
 * This function concatenates two strings with a given separator and returns the result.
 *
 * @param str1 The first string
 * @param str2 The second string
 * @param sep The separator to be used for concatenation
 * @return The concatenated string
 *
 * Example:
 * concatenateString("Hello", "World", ", ") // Output: "Hello, World"
 */
fun concatenateString(str1: String?, str2: String?, sep: String): String? {

    if (str1 == null || str2 == null) {
        return null
    }

    if (str1 !is String || str2 !is String || sep !is String) {
        return null
    }

    return str1 + sep + str2
}
/**
 * This function concatenates two strings with a given separator and returns the result.
 *
 * @param str1 The first string
 * @param str2 The second string
 * @param sep The separator to be used for concatenation
 * @return The concatenated string
 *
 * Example:
 * concatenateString("Hello", "World", ", ") // Output: "Hello, World"
 */
fun concatenateString(str1: String?, str2: String?, sep: String): String? {
/**
 * This function concatenates two strings with a given separator and returns the result.
 *
 * @param str1 The first string
 * @param str2 The second string
 * @param sep The separator to be used for concatenation
 * @return The concatenated string
 *
 * Example:
 * concatenateString("Hello", "World", ", ") // Output: "Hello, World"
 */
fun concatenateString(str1: String?, str2: String?, sep: String): String? {

    if (str1 == null || str2 == null) {
        return null
    }

    if (str1 !is String || str2 !is String || sep !is String) {
        return null
    }

    return str1 + sep + str2
}