fix must be nullable in all cases if produces nulls

Author: ptravers

src/expr/src/scalar/func.rs

@@ -8207,9 +8207,7 @@ impl VariadicFunc {
                 ScalarType::Array(Box::new(ScalarType::String)).nullable(in_nullable)
             }
             RegexpReplace => ScalarType::String.nullable(in_nullable),
-            StringToArray => {
-                ScalarType::Array(Box::new(ScalarType::String)).nullable(input_types[0].nullable)
-            }
+            StringToArray => ScalarType::Array(Box::new(ScalarType::String)).nullable(true),
         }
     }