code: protected boolean mayBeNestedBeanType(Class<?> fieldType) {
          return !fieldType.isPrimitive() // not primitive types
                  && !fieldType.isArray() // not array type, array's nested bean is unsupported for the check, simply
                  && !Object.class.equals(fieldType) // e.g. generic type
                  && !String.class.isAssignableFrom(fieldType) // not String
                  && !Number.class.isAssignableFrom(fieldType) // not Integer, Long, ...
                  && !TemporalAccessor.class.isAssignableFrom(fieldType) // not LocalDate, ...
                  && !java.util.Date.class.isAssignableFrom(fieldType) // not old date
                  && !Boolean.class.isAssignableFrom(fieldType) // not boolean
                  && !Classification.class.isAssignableFrom(fieldType) // not CDef
                  && !File.class.isAssignableFrom(fieldType) // not File
                  && !isCollectionFamilyType(fieldType); // not Collection family
      }
docs: -----------