[ENSCORESW-433]. Fixed ambigous error when an ID lookup has failed. Also improved error detection for symbol lookup
[ENSCORESW-433]. Fixed ambigous error when an ID lookup has failed. Also improved error detection for symbol lookup

helensch/ensembl-rest,ens-lgil/ensembl-rest,helensch/ensembl-rest,helensch/ensembl-rest,willmclaren/ensembl-rest,helensch/ensembl-rest,willmclaren/ensembl-rest,willmclaren/ensembl-rest,willmclaren/ensembl-rest,willmclaren/ensembl-rest,ens-lgil/ensembl-rest,helensch/ensembl-rest,ens-lgil/ensembl-rest,ens-lgil/ensembl-rest,ens-lgil/ensembl-rest