An AI has infected a text with a character!! 
This text is now **fully mutated** to this character.
If the text or the character are empty, return an empty string.  
There will never be a case when both are empty as nothing is going on!!
**Note:** The character is a string of length 1 or an empty string.
# Example
```python
text before = "abc"
character   = "z"
text after  = "zzz"
```
contamination=lambda t,c: c*len(t)
contamination=lambda t,c: c*len(t)