Give a descriptive error message when the 'field' type is invalid.

Author: jtibshirani

x-pack/plugin/vectors/src/main/java/org/elasticsearch/xpack/vectors/query/ScoreScriptUtils.java

@@ -75,12 +75,15 @@ public DenseVectorFunction(ScoreScript scoreScript,
                 }
             }
 
-            if (field instanceof DenseVectorScriptDocValues) {
+            if (field instanceof String) {
+                String fieldName = (String) field;
+                docValues = (DenseVectorScriptDocValues) scoreScript.getDoc().get(fieldName);
+            } else if (field instanceof DenseVectorScriptDocValues) {
                 docValues = (DenseVectorScriptDocValues) field;
                 deprecationLogger.deprecatedAndMaybeLog("vector_function_signature", DEPRECATION_MESSAGE);
             } else {
-                String fieldName = (String) field;
-                docValues = (DenseVectorScriptDocValues) scoreScript.getDoc().get(fieldName);
+                throw new IllegalArgumentException("For vector functions, the 'field' argument must be of type String or " +
+                    "VectorScriptDocValues");
             }
         }
 
@@ -230,12 +233,15 @@ public SparseVectorFunction(ScoreScript scoreScript,
             // Sort dimensions in the ascending order and sort values in the same order as their corresponding dimensions
             sortSparseDimsFloatValues(queryDims, queryValues, n);
 
-            if (field instanceof SparseVectorScriptDocValues) {
+            if (field instanceof String) {
+                String fieldName = (String) field;
+                docValues = (SparseVectorScriptDocValues) scoreScript.getDoc().get(fieldName);
+            } else if (field instanceof SparseVectorScriptDocValues) {
                 docValues = (SparseVectorScriptDocValues) field;
                 deprecationLogger.deprecatedAndMaybeLog("vector_function_signature", DEPRECATION_MESSAGE);
             } else {
-                String fieldName = (String) field;
-                docValues = (SparseVectorScriptDocValues) scoreScript.getDoc().get(fieldName);
+                throw new IllegalArgumentException("For vector functions, the 'field' argument must be of type String or " +
+                    "VectorScriptDocValues");
             }
 
             deprecationLogger.deprecatedAndMaybeLog("sparse_vector_function", SparseVectorFieldMapper.DEPRECATION_MESSAGE);