I created a model matrix. 
Created in it column headers and row headers from ObjDef objects (functions and roles) taken from the outFolder folder. 
I placed the functions on rows, and placed the roles in columns. 
Next, I'm trying to create connections between some functions and roles. Before creating the connection function, I check the contents of the row header and column header with MsgBox. But when calling the

"matrix.createCxn (aHeaderCol [0], aHeaderRow [0], Constants.CT_EXEC_2);"

method, a window with the

"Wrapped java.lang.NullPointerException"

error appears. 

Tell me please what I'm doing wrong.

Here is the code:

function main() {
     var db = ArisData.getActiveDatabase();
     var group = ArisData.getSelectedGroups()[0];
     var outFolder = db.Group(["Main_group", "Work folders", "Test", "Matrix", "output_1"], 1049);
     var aFuncs = group.ObjDefListFilter ( 22 );   // Functions ObjDefs
     var aRoles = group.ObjDefListFilter ( 78 );   // Roles ObjDefs
     var oModel = outFolder.CreateModel(220,"Matrix_model",1049);
     var matrix = oModel.getMatrixModel();
     var Row_matrixHeader = matrix.getHeader(true);
     var Column_matrixHeader = matrix.getHeader(false);
     var Row_Header_Title = Row_matrixHeader.setTitle("Functions",1049);   
     var Column_Header_Title = Column_matrixHeader.setTitle("Roles",1049);
     // Creating header row cells
     for(var i=0; i < aFuncs.length; i++) {  
         matrix.createHeaderCell(null, aFuncs[i], Constants.ST_FUNC, -1, true);
         matrix.setVisibleObjectSymbolTypes([Constants.ST_FUNC], true);
    // Creating header column cells
    for(var i=0; i < aRoles.length; i++) {  
         matrix.createHeaderCell(null, aRoles[i], Constants.ST_EMPL_TYPE, -1, false);
         matrix.setVisibleObjectSymbolTypes([Constants.ST_EMPL_TYPE], false);
    var aHeaderCol = Column_matrixHeader.getCells();
    var aHeaderRow = Row_matrixHeader.getCells();
    Dialogs.MsgBox("aHeaderCol[0]: " + aHeaderCol[0].getDefinition().Attribute(Constants.AT_NAME, 1049).getValue());  //OK
    Dialogs.MsgBox("aHeaderRow[0]: " + aHeaderRow[0].getDefinition().Attribute(Constants.AT_NAME, 1049).getValue());  //OK

    matrix.createCxn( aHeaderCol[0], aHeaderRow[0], Constants.CT_EXEC_2 );   //  <- Error