Support storeNullValue and storeEmptyValue for property that is annotated with @MultiField annotation

[donghuantang]

Currently storeNullValue and storeEmptyValue are supported for property that is annotated with the @field annotation. Need to also add support for property that is annotated with @MultiField annotation. Suggesting the following code change in the SimpleElasticsearchPersistentProperty class:

In the SimpleElasticsearchPersistentProperty constructer, update the assignment of storeNullValue and storeEmptyValue to also check the mainField parameters in the @MultiField annotation:

storeNullValue = (isField && getRequiredAnnotation(Field.class).storeNullValue()) || (isAnnotationPresent(MultiField.class) && getRequiredAnnotation(MultiField.class).mainField().storeNullValue()); storeEmptyValue = isField ? getRequiredAnnotation(Field.class).storeEmptyValue() : isAnnotationPresent(MultiField.class) ? getRequiredAnnotation(MultiField.class).mainField().storeEmptyValue() : true;