feat(gemini) not null checks on safetySettings

Author: terussell85

models/spring-ai-vertex-ai-gemini/src/main/java/org/springframework/ai/vertexai/gemini/VertexAiGeminiChatOptions.java

@@ -279,6 +279,7 @@ public List<SafetySetting> getSafetySettings() {
 	}
 
 	public void setSafetySettings(List<SafetySetting> safetySettings) {
+		Assert.notNull(safetySettings, "safetySettings must not be null");
 		this.safetySettings = safetySettings;
 	}
 
@@ -422,6 +423,7 @@ public Builder withGoogleSearchRetrieval(boolean googleSearch) {
 		}
 
 		public Builder withSafetySettings(List<SafetySetting> safetySettings) {
+			Assert.notNull(safetySettings, "safetySettings must not be null");
 			this.options.safetySettings = safetySettings;
 			return this;
 		}