refactor(udf): null-guard registerUdf arguments and drop dead assertion

Author: andygrove

core/src/main/java/org/apache/datafusion/SessionContext.java

@@ -229,6 +229,11 @@ public void registerUdf(
     if (nativeHandle == 0) {
       throw new IllegalStateException("SessionContext is closed");
     }
+    java.util.Objects.requireNonNull(name, "name");
+    java.util.Objects.requireNonNull(udf, "udf");
+    java.util.Objects.requireNonNull(returnType, "returnType");
+    java.util.Objects.requireNonNull(argTypes, "argTypes");
+    java.util.Objects.requireNonNull(volatility, "volatility");
     List<Field> fields = new ArrayList<>(argTypes.size() + 1);
     fields.add(new Field("return", FieldType.nullable(returnType), null));
     for (int i = 0; i < argTypes.size(); i++) {

core/src/test/java/org/apache/datafusion/ScalarUdfTest.java

@@ -20,7 +20,6 @@
 package org.apache.datafusion;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertNotNull;
 
 import java.util.List;
 
@@ -79,7 +78,6 @@ void addOne_overConstantTable_returnsIncrementedValues() throws Exception {
         assertEquals(2, y.get(0));
         assertEquals(3, y.get(1));
         assertEquals(4, y.get(2));
-        assertNotNull(y);
       }
     }
   }