Steps to reproduce:

• 1st request

  {"jsonrpc":"2.0","method":"configuration.import","params":{"format":"xml","rules":{"screens":{"createMissing":true}},"source":"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n\t\t\t\t\t\t\t\t<zabbix_export>\n\t\t\t\t\t\t\t\t<version>3.2<\/version>\n\t\t\t\t\t\t\t\t<date>2016-12-12T07:18:00Z<\/date>\n\t\t\t\t\t\t\t\t<screens>\n\t\t\t\t\t\t\t\t\t<screen>\n\t\t\t\t\t\t\t\t\t\t<name>API screen xml import<\/name>\n\t\t\t\t\t\t\t\t\t\t<hsize>1<\/hsize>\n\t\t\t\t\t\t\t\t\t\t<vsize>1<\/vsize>\n\t\t\t\t\t\t\t\t\t<\/screen>\n\t\t\t\t\t\t\t\t<\/screens>\n\t\t\t\t\t\t\t\t<\/zabbix_export>"},"id":0,"auth":"152368e35c55fd4c019c137457e73854"}

  Undefined index: updateExisting [api_jsonrpc.php:63 -> CJsonRpc->execute() -> CLocalApiClient->callMethod() -> call_user_func_array() -> CConfiguration->import() -> CConfigurationImport->import() -> CConfigurationImport->processScreens() -> CConfigFile->{closure}() in include/classes/import/CConfigurationImport.php:1697]
  Undefined index: updateExisting [api_jsonrpc.php:63 -> CJsonRpc->execute() -> CLocalApiClient->callMethod() -> call_user_func_array() -> CConfiguration->import() -> CConfigurationImport->import() -> CConfigurationImport->processScreens() -> CScreenImporter->import() -> CConfigFile->{closure}() in include/classes/import/importers/CScreenImporter.php:63]

• 2nd request

  {"jsonrpc":"2.0","method":"configuration.import","params":{"format":"xml","rules":{"valueMaps":{"createMissing":true}},"source":"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n\t\t\t\t\t\t\t\t<zabbix_export>\n\t\t\t\t\t\t\t\t<version>3.2<\/version>\n\t\t\t\t\t\t\t\t<date>2016-12-12T07:18:00Z<\/date>\n\t\t\t\t\t\t\t\t<value_maps>\n\t\t\t\t\t\t\t\t\t<value_map>\n\t\t\t\t\t\t\t\t\t\t<name>API valueMap xml import<\/name>\n\t\t\t\t\t\t\t\t\t\t<mappings>\n\t\t\t\t\t\t\t\t\t\t\t<mapping>\n\t\t\t\t\t\t\t\t\t\t\t\t<value>1<\/value>\n\t\t\t\t\t\t\t\t\t\t\t\t<newvalue>Up<\/newvalue>\n\t\t\t\t\t\t\t\t\t\t\t<\/mapping>\n\t\t\t\t\t\t\t\t\t\t<\/mappings>\n\t\t\t\t\t\t\t\t\t<\/value_map>\n\t\t\t\t\t\t\t\t<\/value_maps>\n\t\t\t\t\t\t\t\t<\/zabbix_export>"},"id":0,"auth":"cc591070c53a846bb1163ef9d33221f5"}

  Undefined index: updateExisting [api_jsonrpc.php:63 -> CJsonRpc->execute() -> CLocalApiClient->callMethod() -> call_user_func_array() -> CConfiguration->import() -> CConfigurationImport->import() -> CConfigurationImport->processValueMaps() -> CConfigFile->{closure}() in include/classes/import/CConfigurationImport.php:655]