no null values in ingest configuration error messages (#20616)

The invalid ingest configuration field name used to show itself,
even when it was null, in error messages. Sometimes this does not make
sense.

e.g.
```[null] Only one of [file], [id], or [inline] may be configure```
vs.
```Only one of [file], [id], or [inline] may be configure```

The above deals with three fields, therefore this no one property
responsible.

core/src/main/java/org/elasticsearch/ingest/ConfigurationUtils.java

@@ -224,7 +224,13 @@ public final class ConfigurationUtils {
 
     public static ElasticsearchException newConfigurationException(String processorType, String processorTag,
                                                                         String propertyName, String reason) {
-        ElasticsearchParseException exception = new ElasticsearchParseException("[" + propertyName + "] " + reason);
+        String msg;
+        if (propertyName == null) {
+           msg = reason;
+        } else {
+            msg = "[" + propertyName + "] " + reason;
+        }
+        ElasticsearchParseException exception = new ElasticsearchParseException(msg);
         addHeadersToException(exception, processorType, processorTag, propertyName);
         return exception;
     }

modules/ingest-common/src/test/java/org/elasticsearch/ingest/common/ScriptProcessorFactoryTests.java

@@ -56,7 +56,7 @@ public class ScriptProcessorFactoryTests extends ESTestCase {
 
         ElasticsearchException exception = expectThrows(ElasticsearchException.class,
             () -> factory.create(null, randomAsciiOfLength(10), configMap));
-        assertThat(exception.getMessage(), is("[null] Only one of [file], [id], or [inline] may be configured"));
+        assertThat(exception.getMessage(), is("Only one of [file], [id], or [inline] may be configured"));
     }
 
     public void testFactoryValidationAtLeastOneScriptingType() throws Exception {
@@ -66,6 +66,6 @@ public class ScriptProcessorFactoryTests extends ESTestCase {
         ElasticsearchException exception = expectThrows(ElasticsearchException.class,
             () -> factory.create(null, randomAsciiOfLength(10), configMap));
 
-        assertThat(exception.getMessage(), is("[null] Need [file], [id], or [inline] parameter to refer to scripts"));
+        assertThat(exception.getMessage(), is("Need [file], [id], or [inline] parameter to refer to scripts"));
     }
 }