Dropdown LIst throwing error while loading

Hi All,

One of the Dropdown List is throwing error while loading, but this seems to be working with other Dropdown lists.

Dropdown default loads with master data from tables, when I click new button to create a transaction record black form needs to open and dropdown should display blank and loaded with master data

I handled null, no luck its always throwing attached errors.

also attached results from backend.

dropdown code as follows(highlighted red Value tag which causing the issue) 

====================

rule!GLOB_dropdownFieldRefValues(
            label: "Material Grade (Master Data)",
            allChoiceLabels: ri!MaterailGradeData.DESCRIPTION ,
            allChoiceValues: ri!MaterailGradeData.DATA_ID,
            value:ri!EWR_EPMPARFPipelineList[ri!selectedRow_int].MATERIAL_GRADE_VALUE,
            saveInto:ri!EWR_EPMPARFPipelineList[ri!selectedRow_int].MATERIAL_GRADE_VALUE,
            placeholderLabel: "",
            activeChoiceLabels: index(ri!MaterailGradeData.DESCRIPTION,wherecontains(ri!EWR_EPMPARFPipelineList[ri!selectedRow_int].MATERIAL_GRADE, ri!MaterailGradeData.GRADE_ID)),
            activeChoiceValues: index(ri!MaterailGradeData.DATA_ID, wherecontains(ri!EWR_EPMPARFPipelineList[ri!selectedRow_int].MATERIAL_GRADE, ri!MaterailGradeData.GRADE_ID))
          )}),

Appreciate any help/suggestions..