Map UDF : The Nothing type cannot have a serializer

[shkob1]

Hey,

As im building a SQL query, im trying to conditionally build a map such that
there won't be any keys with null values in it. AFAIK from Calcite there's
no native way to do it (other than using case to build the map in different
ways, but then i have a lot of key/value pairs so thats not reasonable). I
tried to implement it using a flink UDF but failed - i wonder if a table
function can return a map since im getting "The Nothing type cannot have a
serializer".

Example SQL:

Select a, b, c, removeNulls('key1', d, 'key2', e, 'key3', f) AS my_map
FROM... 

My Table Function code is:

public class RemoveNullValuesFunction extends
TableFunction<Map&lt;String,String>> {

    public static final String NAME = "removeNulls";

    public void eval(String... keyValues) {

        if (keyValues.length == 0) {
            collect(Collections.emptyMap());
            return;
        }
        final List<String> keyValuesList = Arrays.asList(keyValues);
        Map<String,String> output = Maps.newHashMap();
        for (int i = 0; i < keyValuesList.size(); i = i + 2){
            final String key = keyValuesList.get(i);
            final String value = keyValuesList.get(i + 1);
            if (value != null)
                output.put(key, value);
        }
        collect(output);

    }

    @Override
    public TypeInformation<Map&lt;String, String>> getResultType() {
        return Types.MAP(Types.STRING(),Types.STRING());
    }
}


I wonder if thats not possible or am i missing something in how the
serialization works?

Thanks!
Shahar







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