**Debug** a function called calculate that takes 3 values. The first and third values are numbers. The second value is a character. If the character is "+" , "-", "\*", or "/", the function will return the result of the corresponding mathematical function on the two numbers. If the string is not one of the specified characters, the function should return null.
```
calculate(2,"+", 4); //Should return 6
calculate(6,"-", 1.5); //Should return 4.5
calculate(-4,"*", 8); //Should return -32
calculate(49,"/", -7); //Should return -7
calculate(8,"m", 2); //Should return null
calculate(4,"/",0) //should return null
```
Kind of a fork (not steal :)) of [Basic Calculator][1] kata by [TheDoctor][2]. 
[1]: http://www.codewars.com/kata/basic-calculator/javascript
[2]: http://www.codewars.com/users/528c45adbd9daa384300068d
calculate = lambda a,o,b, m=__import__("operator"): None if o not in "+-*/" or o=='/' and not b else {"+":m.__add__, "-":m.__sub__, "*":m.__mul__, "/":m.__truediv__}[o](a, b)
calculate = lambda a,o,b, m=__import__("operator"): None if o not in "+-*/" or o=='/' and not b else {"+":m.__add__, "-":m.__sub__, "*":m.__mul__, "/":m.__truediv__}[o](a, b)