my code is filling with the same element on return and I dont know why

Running sort: Heap K$-$Way Merge with $8$ items

$52843716$

firstIndex: $0,$ lastIndex: $8$

numValues: $8,$ subarraySize: $4,$ remaining: $0$

firstIndex: $0,$ lastIndex: $4$

numValues: $4,$ subarraySize: $2,$ remaining: $0$

firstIndex: $0,$ lastIndex: $2$

numValues: $2,$ subarraySize: $1,$ remaining: $0$

Constructing MinHeap...

Source Array Size: $2$

Source Array: $52$

Adding Subarray to Heap...

Subarray Contents: $5$

Adding Subarray to Heap...

Subarray Contents: $2$

Merging sorted subarrays:

Smallest element: $2$

Smallest element: $2$

firstIndex: $2,$ lastIndex: $4$

numValues: $2,$ subarraySize: $1,$ remaining: $0$

Constructing MinHeap...

Source Array Size: $2$

Source Array: $22$

Adding Subarray to Heap...

Subarray Contents: $2$

Adding Subarray to Heap...

Subarray Contents: $2$

Merging sorted subarrays:

Smallest element: $2$

Smallest element: $2$

Constructing MinHeap...

Source Array Size: $4$

Source Array: $2222$

Adding Subarray to Heap...

Subarray Contents: $22$

Adding Subarray to Heap...

Subarray Contents: $22$

Merging sorted subarrays:

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

firstIndex: $4,$ lastIndex: $8$

numValues: $4,$ subarraySize: $2,$ remaining: $0$

firstIndex: $4,$ lastIndex: $6$

numValues: $2,$ subarraySize: $1,$ remaining: $0$

Constructing MinHeap...

Source Array Size: $2$

Source Array: $22$

Adding Subarray to Heap...

Subarray Contents: $2$

Adding Subarray to Heap...

Subarray Contents: $2$

Merging sorted subarrays:

Smallest element: $2$

Smallest element: $2$

firstIndex: $6,$ lastIndex: $8$

numValues: $2,$ subarraySize: $1,$ remaining: $0$

Constructing MinHeap...

Source Array Size: $2$

Source Array: $22$

Adding Subarray to Heap...

Subarray Contents: $2$

Adding Subarray to Heap...

Subarray Contents: $2$

Merging sorted subarrays:

Smallest element: $2$

Smallest element: $2$

Constructing MinHeap...

Source Array Size: $4$

Source Array: $2222$

Adding Subarray to Heap...

Subarray Contents: $22$

Adding Subarray to Heap...

Subarray Contents: $22$

Merging sorted subarrays:

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

Constructing MinHeap...

Source Array Size: $8$

Source Array: $22222222$

Adding Subarray to Heap...

Subarray Contents: $2222$

Adding Subarray to Heap...

Subarray Contents: $2222$

Merging sorted subarrays:

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

Smallest element: $2$

$22222222$

Sorted!

Sort completed in $35\mathrm{.}008$ milliseconds

Passed Test $1.$ Merge sort

$----------------$

Passed $1$ out of $4$ group tests

$--$End of tests$-$