fix: Unknown enum values/names should result in nulls and not exceptions

src/main/java/graphql/schema/GraphQLEnumType.java

@@ -1,7 +1,6 @@
 package graphql.schema;
 
 
-import graphql.GraphQLException;
 import graphql.language.EnumValue;
 
 import java.util.ArrayList;
@@ -40,15 +39,15 @@ public Object parseLiteral(Object input) {
 
     private Object getValueByName(Object value) {
         GraphQLEnumValueDefinition enumValueDefinition = valueDefinitionMap.get(value);
-        if (enumValueDefinition.getValue() != null) return enumValueDefinition.getValue();
-        throw new GraphQLException("");
+        if (enumValueDefinition != null) return enumValueDefinition.getValue();
+        return null;
     }
 
     private Object getNameByValue(Object value) {
         for (GraphQLEnumValueDefinition valueDefinition : valueDefinitionMap.values()) {
             if (value.equals(valueDefinition.getValue())) return valueDefinition.getName();
         }
-        throw new GraphQLException("");
+        return null;
     }
 
     public List<GraphQLEnumValueDefinition> getValues() {

src/test/groovy/graphql/schema/GraphQLEnumTypeTest.groovy

@@ -0,0 +1,40 @@
+package graphql.schema
+
+import spock.lang.Specification
+
+import static graphql.schema.GraphQLEnumType.newEnum
+
+
+class GraphQLEnumTypeTest extends Specification {
+
+    GraphQLEnumType enumType
+
+    def setup() {
+        enumType = newEnum().name("TestEnum")
+                .value("NAME", 42)
+                .build();
+    }
+
+    def "parse value returns null for unknown value"() {
+        expect:
+        enumType.getCoercing().parseValue("UNKNOWN") == null
+    }
+
+
+    def "parse value return value for the name"() {
+        expect:
+        enumType.getCoercing().parseValue("NAME") == 42
+    }
+
+    def "serialize returns name for value"() {
+        expect:
+        enumType.getCoercing().serialize(42) == "NAME"
+    }
+
+    def "serialize returns null for unknown value"() {
+        expect:
+        enumType.getCoercing().serialize(12) == null
+    }
+
+
+}