eth_filter fix lint and tests

src/test/groovy/io/emeraldpay/dshackle/upstream/calls/EthereumCallSelectorSpec.groovy

@@ -193,8 +193,19 @@ class EthereumCallSelectorSpec extends Specification {
         param | hash
         '["0xff09"]' | 9
         '["0xff"]' | 255
-        '[]' | 0
         '[""]' | 0
         '["0x0"]' | 0
     }
+
+    def "Get empty matcher for getFilterChanges method without params"() {
+        setup:
+        def callSelector = new EthereumCallSelector(Mock(Reader))
+        def head = Mock(Head)
+
+        when:
+        def act = callSelector.getMatcher("eth_getFilterChanges", "[]", head).block()
+
+        then:
+        act == null
+    }
 }