Say hello!

Write a function to greet a person. Function will take name as input and greet the person by saying hello.
Return null/nil/None if input is empty string or null/nil/None.

Example: 

```python
greet("Niks") --> "hello Niks!"
greet("")    --> None # Return None if input is empty string
greet(None)  --> None # Return None if input is None
```

Difficulty: EASY
Starter code: def greet(name):
	

Solutions:
def greet(name):
	return f'hello {name}!' if name else None


def greet(name):
	if name:
		return f'hello {name}!'


def greet(s):
	if s:
		return f'hello {s}!'


def greet(name=None):
	return 'hello {}!'.format(name) if name else None


def greet(n):
	if n:
		return f'hello {n}!'


def greet(name):
	if name == None:
		return None
	if name == '':
		return None
	n = len(name)
	if n >= 1:
		return 'hello' + ' ' + name + '!'


def greet(name):
	if name == None:
		return None
	if len(name) > 0:
		return 'hello ' + name + '!'
	else:
		return None


def greet(name):
	if name == '':
		return None
	elif isinstance(name, str):
		return 'hello ' + name + '!'
	else:
		return None


def greet(name):
	if name is '' or name is None:
		return None
	else:
		return f'hello {name}!'


def greet(name):
	if name in ['', None]:
		return None
	return f'hello {name}!'