java - How to get rid of null elements from inner arrayList in 2 dimensional arrayList -

i have following of type arraylist<list<string>>

array_acidexp[[statistics (ph), upright, recumbent, total], [upright, normal, recumbent, normal, total, normal], [clearance ph  :  channel 7], [minimum, 4.69, , 2.42], [maximum, 7.88, , 7.51, , 7.88], [mean, 6.33, , 6.41, , 6.37], [median, 6.62, , 6.40, , 6.49]] 

i have tried following without luck:

 (int = 0; < arr_acidexp_pattern_table2d.size(); i++) { arr_acidexp_pattern_table2d.removeall(collections.singleton(null)); arr_acidexp_pattern_table2d.get(i).removeall(collections.singleton(" "));              } 

what should rid of empty elements?

this remove internal nulls

 (list<string> internal : array_acidexp) {         if (internal != null) {             (int = 0; < internal.size(); i++) {                 if (internal.get(i) == null) {                     internal.remove(i)                 }             }         }     } 

did not run ...