This CL modify the `evalExpr()` of ExpressionFunctions, so that it won't change the `FunctionCallExpr` to `NullLiteral` when there is null parameter in UDF. Which will fix the problem described in ISSUE: #2913
This CL modify the `evalExpr()` of ExpressionFunctions, so that it won't change the `FunctionCallExpr` to `NullLiteral` when there is null parameter in UDF. Which will fix the problem described in ISSUE: #2913