Fix NPE with schema yaml convert (#8124)

shardingsphere-governance/shardingsphere-governance-core/shardingsphere-governance-core-common/src/main/java/org/apache/shardingsphere/governance/core/yaml/config/schema/YamlTableMetaData.java

@@ -22,6 +22,7 @@ import lombok.Setter;
 import org.apache.shardingsphere.infra.yaml.config.YamlConfiguration;
 
 import java.util.Collection;
+import java.util.LinkedHashSet;
 import java.util.Map;
 
 /**
@@ -35,5 +36,5 @@ public final class YamlTableMetaData implements YamlConfiguration {
     
     private Map<String, YamlIndexMetaData> indexes;
     
-    private Collection<String> addressingDataSources;
+    private Collection<String> addressingDataSources = new LinkedHashSet<>();
 }