Data flow style change from if-else to water flow.

core/src/main/java/org/springframework/security/access/expression/method/ExpressionBasedPreInvocationAdvice.java

@@ -56,27 +56,42 @@ public boolean before(Authentication authentication, MethodInvocation mi, PreInv
 	}
 
 	private Object findFilterTarget(String filterTargetName, EvaluationContext ctx, MethodInvocation invocation) {
-		Object filterTarget = null;
+		Object filterTarget;
+
 		if (filterTargetName.length() > 0) {
 			filterTarget = ctx.lookupVariable(filterTargetName);
 			Assert.notNull(filterTarget,
-					() -> "Filter target was null, or no argument with name " + filterTargetName + " found in method");
-		}
-		else if (invocation.getArguments().length == 1) {
-			Object arg = invocation.getArguments()[0];
-			if (arg.getClass().isArray() || arg instanceof Collection<?>) {
-				filterTarget = arg;
-			}
-			Assert.notNull(filterTarget, () -> "A PreFilter expression was set but the method argument type"
-					+ arg.getClass() + " is not filterable");
+					() -> new StringBuilder("Filter target was null, or no argument with name ").append(filterTargetName).append(" found in method").toString());
+			assertIsNotOfTypeArray(filterTarget);
+
+			return filterTarget;
 		}
-		else if (invocation.getArguments().length > 1) {
+
+		Object[] args = invocation.getArguments();
+
+		if (args.length > 1) {
 			throw new IllegalArgumentException(
 					"Unable to determine the method argument for filtering. Specify the filter target.");
 		}
+
+		if (args.length == 1 && firstArgIsArrayOrCollection(args[0])) {
+			filterTarget = args[0];
+			Assert.notNull(filterTarget, () -> new StringBuilder("A PreFilter expression was set but the method argument type")
+					.append(args[0].getClass()).append(" is not filterable").toString());
+			assertIsNotOfTypeArray(filterTarget);
+			return filterTarget;
+		}
+
+		throw new IllegalStateException("Unexpected either filterTargetName or invocation arguments provided. Provide either the target name or invocation argument with one argument");
+	}
+
+	private boolean firstArgIsArrayOrCollection(Object arg) {
+		return arg.getClass().isArray() || arg instanceof Collection<?>;
+	}
+
+	private void assertIsNotOfTypeArray(Object filterTarget) {
 		Assert.isTrue(!filterTarget.getClass().isArray(),
 				"Pre-filtering on array types is not supported. Using a Collection will solve this problem");
-		return filterTarget;
 	}
 
 	public void setExpressionHandler(MethodSecurityExpressionHandler expressionHandler) {