problem: unable to run without default options

src/main/kotlin/io/emeraldpay/dshackle/config/UpstreamsConfigReader.kt

@@ -201,7 +201,8 @@ class UpstreamsConfigReader {
     }
 
     private fun <T> getList(mappingNode: MappingNode?, key: String): CollectionNode<T>? {
-        return getValue(mappingNode, key, CollectionNode::class.java) as CollectionNode<T>
+        val value = getValue(mappingNode, key, CollectionNode::class.java) ?: return null
+        return value as CollectionNode<T>
     }
 
     private fun getListOfString(mappingNode: MappingNode?, key: String): List<String>? {

src/test/groovy/io/emeraldpay/dshackle/config/UpstreamsConfigReaderSpec.groovy

@@ -136,4 +136,27 @@ class UpstreamsConfigReaderSpec extends Specification {
         "\${PASSWORD}"      | "1a68f20154fc258fe4149c199ad8f281"
     }
 
+    def "Parse config without defaults"() {
+        setup:
+        def config = this.class.getClassLoader().getResourceAsStream("upstreams-no-defaults.yaml")
+        when:
+        def act = reader.read(config)
+        then:
+        act != null
+        act.version == "v1"
+        with(act.defaultOptions) {
+            size() == 0
+        }
+        act.upstreams.size() == 1
+        with(act.upstreams.get(0)) {
+            id == "local"
+            chain == "ethereum"
+            connection instanceof UpstreamsConfig.EthereumConnection
+            with((UpstreamsConfig.EthereumConnection)connection) {
+                rpc != null
+                rpc.url == new URI("http://localhost:8545")
+                ws == null
+            }
+        }
+    }
 }

src/test/resources/upstreams-no-defaults.yaml

@@ -0,0 +1,9 @@
+version: v1
+
+upstreams:
+  - id: local
+    chain: ethereum
+    connection:
+      ethereum:
+        rpc:
+          url: "http://localhost:8545"