GH-190 Added null check for publisher

Resolves #190

spring-cloud-function-context/src/test/java/org/springframework/cloud/function/context/catalog/InMemoryFunctionCatalogTests.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2016-2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.function.context.catalog;
+
+import static org.junit.Assert.assertSame;
+
+import java.util.function.Function;
+
+import org.junit.Test;
+import org.springframework.cloud.function.context.FunctionRegistration;
+import org.springframework.cloud.function.context.FunctionType;
+
+/**
+ *
+ * @author Oleg Zhurakousky
+ *
+ */
+public class InMemoryFunctionCatalogTests {
+
+	@Test
+	public void testFunctionRegistration() {
+		TestFunction function = new TestFunction();
+		FunctionRegistration<TestFunction> registration = new FunctionRegistration<>(function)
+				.type(FunctionType.of(TestFunction.class).getType());
+		InMemoryFunctionCatalog catalog = new InMemoryFunctionCatalog();
+		catalog.register(registration);
+		FunctionRegistration<?> registration2 = catalog.getRegistration(function);
+		assertSame(registration, registration2);
+	}
+
+	private static class TestFunction implements Function<Integer, String> {
+		@Override
+		public String apply(Integer t) {
+			return "i=" + t;
+		}
+	}
+}