diff --git a/CHANGELOG.md b/CHANGELOG.md
index c0584c57c..6f4dc9b37 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -22,6 +22,7 @@
 * [#2693](https://github.com/ruby-grape/grape/pull/2693): Introduce `Grape::Exceptions::ErrorResponse` value object to replace the implicit-schema Hash thrown via `throw` - [@ericproulx](https://github.com/ericproulx).
 * [#2701](https://github.com/ruby-grape/grape/pull/2701): Replace `.tap` usages in `lib/` with explicit local variables - [@ericproulx](https://github.com/ericproulx).
 * [#2704](https://github.com/ruby-grape/grape/pull/2704): Add `Grape::Endpoint#logger` so the API's configured logger is reachable inside route handlers, filters, and `rescue_from` blocks without a helper - [@ericproulx](https://github.com/ericproulx).
+* [#2707](https://github.com/ruby-grape/grape/pull/2707): Tighten six guard conditions in `lib/` via De Morgan and `blank?`/`present?`/`include?` rewrites; no behaviour change - [@ericproulx](https://github.com/ericproulx).
 * Your contribution here.
 
 #### Fixes
diff --git a/lib/grape/api.rb b/lib/grape/api.rb
index 90824e607..4edae21fd 100644
--- a/lib/grape/api.rb
+++ b/lib/grape/api.rb
@@ -10,8 +10,11 @@ class API
     Helpers = Grape::DSL::Helpers::BaseHelper
 
     class Boolean
+      VALUES = [true, false].freeze
+      private_constant :VALUES
+
       def self.build(val)
-        return nil if val != true && val != false
+        return nil unless VALUES.include?(val)
 
         new
       end
diff --git a/lib/grape/dsl/routing.rb b/lib/grape/dsl/routing.rb
index b8ff0be4d..ca5b5e374 100644
--- a/lib/grape/dsl/routing.rb
+++ b/lib/grape/dsl/routing.rb
@@ -163,7 +163,7 @@ def route(methods, paths = ['/'], route_options = {}, &)
         endpoint_description = inheritable_setting.route[:description]
         all_route_options = { params: endpoint_params }
         all_route_options.deep_merge!(endpoint_description) if endpoint_description
-        all_route_options.deep_merge!(route_options) if route_options&.any?
+        all_route_options.deep_merge!(route_options) if route_options.present?
 
         new_endpoint = Grape::Endpoint.new(
           inheritable_setting,
diff --git a/lib/grape/request.rb b/lib/grape/request.rb
index f972c011a..9cbc14ac5 100644
--- a/lib/grape/request.rb
+++ b/lib/grape/request.rb
@@ -161,9 +161,10 @@ def cookies
     def make_params
       params = @params_builder.call(rack_params)
       routing_args = env[Grape::Env::GRAPE_ROUTING_ARGS]
-      return params unless routing_args&.any? { |k, _| k != :version && k != :route_info }
+      filtered = routing_args&.except(:version, :route_info)
+      return params if filtered.blank?
 
-      params.deep_merge!(routing_args.except(:version, :route_info))
+      params.deep_merge!(filtered)
     rescue *Grape::RACK_ERRORS
       raise Grape::Exceptions::RequestError
     end
diff --git a/lib/grape/validations/params_scope.rb b/lib/grape/validations/params_scope.rb
index b9002a7e7..c209a0644 100644
--- a/lib/grape/validations/params_scope.rb
+++ b/lib/grape/validations/params_scope.rb
@@ -460,9 +460,9 @@ def guess_coerce_type(coerce_type, *values_list)
       end
 
       def check_incompatible_option_values(default, values, except_values)
-        return unless default && !default.is_a?(Proc)
+        return if default.nil? || default.is_a?(Proc)
 
-        raise Grape::Exceptions::IncompatibleOptionValues.new(:default, default, :values, values) if values && !values.is_a?(Proc) && !Array(default).all? { |def_val| values.include?(def_val) }
+        raise Grape::Exceptions::IncompatibleOptionValues.new(:default, default, :values, values) if values && !values.is_a?(Proc) && Array(default).any? { |def_val| !values.include?(def_val) }
 
         return unless except_values && !except_values.is_a?(Proc) && Array(default).any? { |def_val| except_values.include?(def_val) }
 
diff --git a/lib/grape/validations/validators/base.rb b/lib/grape/validations/validators/base.rb
index 3cb947f5c..9d82f575c 100644
--- a/lib/grape/validations/validators/base.rb
+++ b/lib/grape/validations/validators/base.rb
@@ -148,7 +148,7 @@ def option_value
         end
 
         def scrub(value)
-          return value unless value.respond_to?(:valid_encoding?) && !value.valid_encoding?
+          return value if !value.respond_to?(:valid_encoding?) || value.valid_encoding?
 
           value.scrub
         end