Query exposed through Spring-Data-Rest will throw an exception if configured a filter on a List of enums

[antonioT90]

The following line of class ReflectionRepositoryInvoker
result[i] = targetType.isInstance(value) ? value : convert(value, param);
In case of targetType List doesn't verify if the generic element required is an enum or a String, skipping the conversion into List of enum.
Hibernate will throw an exception if we provide at least 2 elements.
The convert method, skipped due to the true condition, would have handled the conversion avoiding the error

spring-data-commons/src/main/java/org/springframework/data/repository/support/ReflectionRepositoryInvoker.java

Line 191 in 0d3cf4a

result[i] = targetType.isInstance(value) ? value : convert(value, param);

I reproduced the error on the following repository:
https://github.com/antonioT90/spring-data-rest-enums-errors-sample

[antonioT90]

The error happens when setting the query parameter in the following way:
?enums=VALUE1&enums=VALUE2
The instruction rawParameters.get(parameterName) will return a List containing both values as separate List (a List of List)
Thus the org.springframework.data.repository.support.ReflectionRepositoryInvoker#unwrapSingleElement method will receive as parameter the List of List, returning the first List (containing just the first value).
The List returned is an instance of List (the targetType), thus it will skip the call to the convert method which would have correctly converted the List of Strings into a List of required enums.

Instead, if we perform the invocation in the following way:
?enums=VALUE1,VALUE2
The instruction rawParameters.get(parameterName) will return a List having just the String VALUE1,VALUE2 as element
Thus the org.springframework.data.repository.support.ReflectionRepositoryInvoker#unwrapSingleElement method will receive as parameter the List of String, returning the string VALUE1,VALUE2.
The String returned is not an instance of List (the targetType), thus it will call the convert method which would successfully handle it.