fix(filtering): Made optional fields accept null values

Author: Otixa

projects/igniteui-angular/src/lib/data-operations/filtering-condition.ts

@@ -908,7 +908,7 @@ export interface IFilteringOperation {
     hidden?: boolean;
     /* blazorCSSuppress */
     /* blazorAlternateType: FilteringOperationLogicHandler */
-    logic: (value: any, searchVal?: any, ignoreCase?: boolean) => boolean;
+    logic?: null | ((value: any, searchVal?: any, ignoreCase?: boolean) => boolean);
 }
 
 /**

projects/igniteui-angular/src/lib/data-operations/filtering-expression.interface.ts

@@ -14,9 +14,9 @@ export enum FilteringLogic {
  */
 export declare interface IFilteringExpression {
     fieldName: string;
-    condition?: IFilteringOperation;
-    conditionName?: string;
-    searchVal?: any;
-    searchTree?: IExpressionTree;
+    condition?: IFilteringOperation | null;
+    conditionName?: string | null;
+    searchVal?: any | null;
+    searchTree?: IExpressionTree | null;
     ignoreCase?: boolean;
 }

projects/igniteui-angular/src/lib/data-operations/filtering-expressions-tree.ts

@@ -11,9 +11,9 @@ export enum FilteringExpressionsTreeType {
 export declare interface IExpressionTree {
     filteringOperands: (IExpressionTree | IFilteringExpression)[];
     operator: FilteringLogic;
-    fieldName?: string;
-    entity?: string;
-    returnFields?: string[];
+    fieldName?: string | null;
+    entity?: string | null;
+    returnFields?: (string | null)[];
 }
 
 /* marshalByValue */