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The validity of the condition: matrix[i][j]==null would depend on the data type of the element in the array.
object references can hold a null value
primitive data type elements can not.
For...

I don't "of course" any code that an OP posts. There are so many different ways to write code that I don't try to guess the problem after seeing 3 lines of code doesn't show what the rest of the...

What is matrix.length[i] ?

You need to look at each row (in a loop) to check if any of the rows have elements.

What is the value of the variable: elements for the array you just posted?
Consider: X*0 = 0 & (0 == 0) is true

What is the value of elements for the array you posted?