Improve validation to also error when es_type used with effectsize=NULL

Co-authored-by: rempsyc <13123390+rempsyc@users.noreply.github.com>

Author: Copilot

R/estimate_contrasts.R

@@ -320,8 +320,12 @@ estimate_contrasts.default <- function(
 
   # Validate es_type usage
   call_args <- match.call()
-  if ("es_type" %in% names(call_args) && !is.null(effectsize) && effectsize != "boot") {
-    insight::format_error("`es_type` can only be used when `effectsize = \"boot\"`.")
+  if ("es_type" %in% names(call_args)) {
+    if (is.null(effectsize)) {
+      insight::format_error("`es_type` can only be used when `effectsize` is specified. Currently `effectsize = NULL`.")
+    } else if (effectsize != "boot") {
+      insight::format_error("`es_type` can only be used when `effectsize = \"boot\"`.")
+    }
   }
 
   if (backend == "emmeans") {

tests/testthat/test-estimate_contrasts_effectsize.R

@@ -83,6 +83,12 @@ test_that("estimate_contrasts - es_type only with effectsize='boot'", {
     "can only be used when"
   )
 
+  # Should error when es_type is used with effectsize = NULL
+  expect_error(
+    estimate_contrasts(model, es_type = "hedges.g", backend = "emmeans"),
+    "can only be used when"
+  )
+  
   # Should work when es_type is used with effectsize = "boot"
   set.seed(100)
   result <- estimate_contrasts(model, effectsize = "boot", es_type = "hedges.g", backend = "emmeans")