Activity Chart Checks : (C4015) Elements containing comparisons of unions: (not supported in Code Generation

(C4015) Elements containing comparisons of unions: (not supported in Code Generation

Error In:
Completeness
Description:
Elements contain comparisons of two union data-items. The comparisons of two unions is ambiguous, because the result depends on which field of the unions is the current field in each.
Erroneous Elements:
Actions, activities, conditions, and events