item.isEmpty() checks only the length of the the string

item.isBlank() checks the length and that all the chars are whitespaces

That means that

• " ".isEmpty() should returns false
• " ".isBlank() should returns true

From the doc of isBlank

Returns true if this string is empty or consists solely of whitespace characters.

In future, you can read documentation and see the code from IDE just click Ctrl+B or Command+B. This is written in documantation for isEmpty method:

/**
 * Returns `true` if this char sequence is empty (contains no characters).
 *
 * @sample samples.text.Strings.stringIsEmpty
 */
@kotlin.internal.InlineOnly
public inline fun CharSequence.isEmpty(): Boolean = length == 0

And for isBlank:

 * Returns `true` if this string is empty or consists solely of whitespace characters.
 *
 * @sample samples.text.Strings.stringIsBlank
 */
public actual fun CharSequence.isBlank(): Boolean = length == 0 || indices.all { this[it].isWhitespace() }