private LogicalExpression getConvertToNullableExpr(List<LogicalExpression> args, MinorType minorType,
FunctionImplementationRegistry registry) {
String funcName = "convertToNullable" + minorType.toString();
FunctionCall funcCall = new FunctionCall(funcName, args, ExpressionPosition.UNKNOWN);
FunctionResolver resolver = FunctionResolverFactory.getResolver(funcCall);
DrillFuncHolder matchedConvertToNullableFuncHolder = registry.findDrillFunction(resolver, funcCall);
if (matchedConvertToNullableFuncHolder == null) {
logFunctionResolutionError(errorCollector, funcCall);