Room TypeConverter and search in the table line

[Kadir]

Please tell me I'm out of control, I don't know what I'm doing.

There's an enveloper:

public class MapConverter {
    @TypeConverter
    public String getStringFromMap(Map<Integer, String> map) {
        if(map!= null) {
            StringBuilder mapAsString = new StringBuilder();
            for (Integer key : map.keySet()) {
                mapAsString.append(key + "=" + map.get(key) + ",");
            }
            return mapAsString.toString();
        } else{
            return null;
        }
    }
@TypeConverter
public Map&lt;Integer, String&gt; getMapFromString(String s) {
    Map&lt;Integer, String&gt; myMap = new HashMap&lt;Integer, String&gt;();
    String[] pairs = s.split(","); // 1 элемент -  0=Элемент 0
    for (int i = 0; i &lt; pairs.length; i++) {
        String pair = pairs[i];
        String[] keyValue = pair.split("=");
        myMap.put(Integer.parseInt(keyValue[0]), keyValue[1]);
    }
    return myMap; 

}

}

Class of object:

@Entity(tableName = "contacts")

public class Contact {

@PrimaryKey(autoGenerate = true)

private int id;
private String name;
private String number;
private String group;
private String subgroup;
private String description;
private int priority;
@TypeConverters(MapConverter.class)
private Map<Integer, String> mapOfGroup;
@TypeConverters(MapConverter.class)
private Map<Integer, String> mapOfSubGroup;

Method DAO

@Query("SELECT * FROM contacts WHERE mapOfGroup LIKE '%' || :nameGroup || '%' ")

Flowable<List<Contact>> getAllContactsOfGroup(String nameGroup);

Nothing comes back. As soon as I haven't tried it. I did. LIKE :nameGroup || '%'In addition to the table adding:

Although the converter has not yet added a line to the method getStringFromMap:

 } else{

return null;

}

The data were not added and made a mistake.
I see that line in an attempt to obtain data:

2021-11-10 23:05:53.782 21564-21564/com.example.contacts D/Throwable get Contacts of Group: Attempt to invoke virtual method 'java.lang.String[] java.lang.String.split(java.lang.String)' on a null object reference

Help me figure this out, please. Thank you.

UPDATE:
I found a mistake when I put it in the converter, I changed it, but I still can't get the data.
New converter:

 @TypeConverter

public String getStringFromMap(Map<Integer, String> map) {

StringBuilder mapAsString = new StringBuilder();

int sizeMap = map.size()-1;

int counter = 0;

for (Integer key : map.keySet()) {

if(counter == sizeMap){

mapAsString.append(key + "=" + map.get(key));

} else {

mapAsString.append(key + "=" + map.get(key) + ",");

}

counter++;

}

return mapAsString.toString();

}

The error comes when:

D/Throwable get Contacts of Group: Index: 0, Size: 0

[shizuka]

In general, it: The problem was in class. Contact Second field private Map<Integer, String> mapOfSubGroup; Also indicated @TypeConverters But at the same time, this field has not been transferred. Map♪ That's why the converter was called twice, the first time he and the field made a mistake, Map null

The Query request itself works as follows: '%' || :nameGroup || '%' and '%' or :nameGroup or '%' ")