#vulnerable code 
                             @SuppressWarnings("unchecked")
	protected void _addMapping(K key, final FieldMapperColumnDefinition<K, S> columnDefinition) {
		final FieldMapperColumnDefinition<K, S> composedDefinition = FieldMapperColumnDefinition.compose(columnDefinition, columnDefinitions.getColumnDefinition(key));
		final K mappedColumnKey = composedDefinition.rename(key);

		if (columnDefinition.getCustomFieldMapper() != null) {
			_addMapper((FieldMapper<S, T>) columnDefinition.getCustomFieldMapper());
		} else {
            final PropertyMeta<T, ?> property = propertyMappingsBuilder.addProperty(mappedColumnKey, composedDefinition);
            if (composedDefinition.isKey() && !property.isSubProperty()) {
                mappingContextFactoryBuilder.addKey(key);
            }
		}
	} 
                            #location 10 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             @SuppressWarnings("unchecked")
	protected void _addMapping(K key, final FieldMapperColumnDefinition<K, S> columnDefinition) {
		final FieldMapperColumnDefinition<K, S> composedDefinition = FieldMapperColumnDefinition.compose(columnDefinition, columnDefinitions.getColumnDefinition(key));
		final K mappedColumnKey = composedDefinition.rename(key);

		if (columnDefinition.getCustomFieldMapper() != null) {
			_addMapper((FieldMapper<S, T>) columnDefinition.getCustomFieldMapper());
		} else {
            final PropertyMeta<T, ?> property = propertyMappingsBuilder.addProperty(mappedColumnKey, composedDefinition);
            if (property != null && composedDefinition.isKey() && !property.isSubProperty()) {
                mappingContextFactoryBuilder.addKey(key);
            }
		}
	}