We should conditionally (if not already registered) register RelationalMappingContext and RelationalConverter (pre-initialized with JdbcCustomConversions) in the configuration extension to provide default beans and to not force users to import JdbcConfiguration
DATAJDBC-243 Using @EnableJdbcRepositories and extending JdbcConfiguration causes duplicate bean registrations
After taking a look: there doesn't seem to be much of a requirement to import/extend JdbcCustomConversion. The only case seems to be if the one wants to use a custom DataAccessStrategy, like when using MyBatis. Because then you actually need access to conversions and context
We now map results of exists queries to a boolean flag to ensure proper decoding. Previously, results were attempted to be mapped onto a primitive type which failed as there's no converter registered for Row to Boolean.