model: Avoid frozen literal warning

lib/fhir_models/bootstrap/model.rb

@@ -39,8 +39,8 @@ def ==(other)
     def method_missing(method_name, *_args, &_block)
       if defined?(self.class::MULTIPLE_TYPES) && self.class::MULTIPLE_TYPES[method_name.to_s]
         self.class::MULTIPLE_TYPES[method_name.to_s].each do |type|
-          type[0] = type[0].upcase
-          value = send("#{method_name}#{type}".to_sym)
+          capitalized_type = "#{type[0].upcase}#{type[1..]}"
+          value = send("#{method_name}#{capitalized_type}".to_sym)
           return value unless value.nil?
         end
         return nil
@@ -284,10 +284,10 @@ def primitive?(datatype, value)
     end
     deprecate :is_primitive?, :primitive?
 
-    def check_binding_uri(uri, value)
+    def check_binding_uri(uri_with_version, value)
       valid = false
       # Strip off the |4.0.0 or |4.0.1 or |2014-03-26 or similar from the ends of URLs
-      uri&.gsub!(/\|[A-Za-z0-9.-]*/, '')
+      uri = uri_with_version&.gsub(/\|[A-Za-z0-9.-]*/, '')
       valueset = versioned_fhir_module::Definitions.get_codes(uri)
 
       if ['http://hl7.org/fhir/ValueSet/mimetypes', 'http://www.rfc-editor.org/bcp/bcp13.txt'].include?(uri)

lib/fhir_models/fhirpath/evaluate.rb

@@ -13,14 +13,14 @@ def self.evaluate(expression, hash, parent = nil)
 
   # Get a value from a hash, with some special handling of
   # self references
-  def self.get(key, hash)
-    return @@context if ['$context', '$resource'].include?(key)
-    return @@parent if key == '$parent'
-    return 'http://unitsofmeasure.org' if key == '%ucum'
-    return 'http://snomed.info/sct' if key == '%sct'
-    return 'http://loinc.org' if key == '%loinc'
-    return key.gsub!(/\A\'|\'\Z/, '') if key.start_with?("'") && key.end_with?("'")
-    key.gsub!(/\A"|"\Z/, '') # remove quotes around path if they exist
+  def self.get(raw_key, hash)
+    return @@context if ['$context', '$resource'].include?(raw_key)
+    return @@parent if raw_key == '$parent'
+    return 'http://unitsofmeasure.org' if raw_key == '%ucum'
+    return 'http://snomed.info/sct' if raw_key == '%sct'
+    return 'http://loinc.org' if raw_key == '%loinc'
+    return raw_key.gsub(/\A\'|\'\Z/, '') if raw_key.start_with?("'") && raw_key.end_with?("'")
+    key = raw_key.gsub(/\A"|"\Z/, '') # remove quotes around path if they exist
     if hash.is_a?(Array)
       response = []
       hash.each do |e|