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How many elements are present in the subset of null set ?

> How many elements are present in the subset of a null set?

This is one the question that appeared in my math exam.

***Definition $1.1$ - Subset:***
    A set $A$ is a subset of set $B$ if all the elements of $A$ are also elements of $B$

***Definition $1.2$ - Null set or Void set or Empty set:***
    If is a set containing no elements

***Definition $1.3$ - Power set:***
    It is the set of all possible subsets of a given set

***Theorem $1.1$:*** Every set is a subset of itself

***Theorem $1.2$:*** Null set is a subset of every set

I think the answer to this question is $0$ because,

$$\mathbf{No.\ of\ subsets} = 2^m$$

So, the number of subsets of a null set (denoted by $\emptyset$) which contains $0$ elements would be $2^0 = 1$ and that subset will be the null set $\emptyset$
itself. Hence, the number of elements in $0$.

But my math teacher told me that the answer is $1$. And her reasoning is as follows, she stated the same that the number of subset of a null set will be $1$ and she represented subset of null set as {$\emptyset$}. So she told the answer to be $1$ as the null set acted as an element in here.

I don't know which of the answers - $0$ or $1$ is correct. There is a debate among me and my teacher about the answers. So, you answers with explanation helps me. Could someone let me know . . .