Difference between null and "in C #

The difference between null and "" in C:

Null is the value not initialized after the variable is defined. If you use the convert function for forced conversion, different values will be obtained. After the integer is forcibly converted, the value is 0, after a string is forcibly converted, the value is ""; ", which indicates that the string data type variable is assigned a value, which is completely different from null. null is a special value that indicates invalid reference.

Finally, I understand the differences between <a href = "javascript: void (null)"> title </a> and <a href = "#"> title </a>:
<A href = "javascript: void (null)"> do not refresh the webpage

<A href = "#"> refresh the current page