better error handling

CRM/Contact/Selector/DataProcessorContactSearch.php

CRM/Dataprocessor/BAO/DataProcessor.php

CRM/Dataprocessor/Form/AggregateField.php

CRM/Dataprocessor/Form/DataProcessor.php

CRM/Dataprocessor/Form/Field.php

CRM/Dataprocessor/Form/Output/AbstractUIOutputForm.php

CRM/Dataprocessor/Form/Source.php

CRM/DataprocessorSearch/Form/AbstractSearch.php

Civi/DataProcessor/DataSpecification/DataSpecification.php

Civi/DataProcessor/Exception/DataSourceNotFoundException.php

Civi/DataProcessor/Exception/FieldNotFoundException.php

...DataProcessor/Exception/InvalidConfigurationException.php

...cessor/FieldOutputHandler/CaseRolesFieldOutputHandler.php

...ssor/FieldOutputHandler/ContactLinkFieldOutputHandler.php

...eldOutputHandler/EventRepeatingInfoFieldOutputHandler.php

...taProcessor/FieldOutputHandler/FileFieldOutputHandler.php

.../FieldOutputHandler/GroupsOfContactFieldOutputHandler.php

...ataProcessor/FieldOutputHandler/RawFieldOutputHandler.php

Civi/DataProcessor/FilterHandler/CaseRoleFilter.php

Civi/DataProcessor/FilterHandler/ContactInGroupFilter.php