Relaxed toolCallArguments validation

There seems to be some models not handling correctly the non-nullability of toolCallArguments when defining a tool call. For example, the Ollama implementation is always null-safe (if no tool argument, then '{}' is used). Other implementations might produce a null value.

This PR relaxes the toolCallArguments validation to support null toolCallArguments within ToolCallingObservationContext.

Fixes gh-3234

Signed-off-by: Thomas Vitale <ThomasVitale@users.noreply.github.com>

Author: ThomasVitale

spring-ai-model/src/main/java/org/springframework/ai/tool/observation/ToolCallingObservationContext.java

@@ -47,14 +47,13 @@ public final class ToolCallingObservationContext extends Observation.Context {
 	private String toolCallResult;
 
 	private ToolCallingObservationContext(ToolDefinition toolDefinition, ToolMetadata toolMetadata,
-			String toolCallArguments, @Nullable String toolCallResult) {
+			@Nullable String toolCallArguments, @Nullable String toolCallResult) {
 		Assert.notNull(toolDefinition, "toolDefinition cannot be null");
 		Assert.notNull(toolMetadata, "toolMetadata cannot be null");
-		Assert.hasText(toolCallArguments, "toolCallArguments cannot be null or empty");
 
 		this.toolDefinition = toolDefinition;
 		this.toolMetadata = toolMetadata;
-		this.toolCallArguments = toolCallArguments;
+		this.toolCallArguments = toolCallArguments != null ? toolCallArguments : "{}";
 		this.toolCallResult = toolCallResult;
 	}
 

spring-ai-model/src/test/java/org/springframework/ai/tool/observation/ToolCallingObservationContextTests.java

@@ -32,11 +32,30 @@ class ToolCallingObservationContextTests {
 
 	@Test
 	void whenMandatoryRequestOptionsThenReturn() {
+		var observationContext = ToolCallingObservationContext.builder()
+			.toolDefinition(ToolDefinition.builder().name("toolA").description("description").inputSchema("{}").build())
+			.build();
+		assertThat(observationContext).isNotNull();
+	}
+
+	@Test
+	void whenToolArgumentsIsNullThenReturn() {
+		var observationContext = ToolCallingObservationContext.builder()
+			.toolDefinition(ToolDefinition.builder().name("toolA").description("description").inputSchema("{}").build())
+			.toolCallArguments(null)
+			.build();
+		assertThat(observationContext).isNotNull();
+		assertThat(observationContext.getToolCallArguments()).isEqualTo("{}");
+	}
+
+	@Test
+	void whenToolArgumentsIsNotNullThenReturn() {
 		var observationContext = ToolCallingObservationContext.builder()
 			.toolDefinition(ToolDefinition.builder().name("toolA").description("description").inputSchema("{}").build())
 			.toolCallArguments("lizard")
 			.build();
 		assertThat(observationContext).isNotNull();
+		assertThat(observationContext.getToolCallArguments()).isEqualTo("lizard");
 	}
 
 	@Test
@@ -55,22 +74,4 @@ void whenToolMetadataIsNullThenThrow() {
 			.build()).isInstanceOf(IllegalArgumentException.class).hasMessageContaining("toolMetadata cannot be null");
 	}
 
-	@Test
-	void whenToolCallInputIsNullThenThrow() {
-		assertThatThrownBy(() -> ToolCallingObservationContext.builder()
-			.toolDefinition(ToolDefinition.builder().name("toolA").description("description").inputSchema("{}").build())
-			.toolCallArguments(null)
-			.build()).isInstanceOf(IllegalArgumentException.class)
-			.hasMessageContaining("toolCallArguments cannot be null or empty");
-	}
-
-	@Test
-	void whenToolCallInputIsEmptyThenThrow() {
-		assertThatThrownBy(() -> ToolCallingObservationContext.builder()
-			.toolDefinition(ToolDefinition.builder().name("toolA").description("description").inputSchema("{}").build())
-			.toolCallArguments("")
-			.build()).isInstanceOf(IllegalArgumentException.class)
-			.hasMessageContaining("toolCallArguments cannot be null or empty");
-	}
-
 }