IconicsTextView java.lang.IllegalArgumentException: Parameter specified as non-null is null
## About this issue

Hello! Seems like the standard **TextView** API:
```
public void setText(CharSequence text, BufferType type)
```
Which is calling:
```
private void setText(CharSequence text, BufferType type,
                         boolean notifyBefore, int oldlen)
```
is designed to accept and handle nullable **text** parameter:
```
if (text == null) {
    text = "";
}
```

However, Kotlin-based **IconicsTextView** requires **text** to be not null:

```
override fun setText(text: CharSequence, type: TextView.BufferType) {
    if (!isInEditMode) {
        super.setText(text.buildIconics(), type)
    } else {
        super.setText(text, type)
    }
}
```

That discrepancy causes issues when working with **IconicsTextView** in the same style as with a typical TextView.
How about making **IconicsTextView** to accept nullable text parameters explicitly?

## Details
- Used library version: 5.0.3
